Hello,
I'm running a development version of Kibana 7.10.2. Currently, I have a fork of EUI 29.3.2, with many custom components (eui/packages/) and themes (eui/src/themes).
Ideally, I want to submodule this fork in kibana/packages/elastic-eui with the awareness of @kbn/pm to do the job. I follow the instruction to make this kibana/packages/elastic-eui/package.json to have private: true.
However yarn kbn bootstrap  throw lots of error regarding dependency version conflicts between kibana and eui:
ERROR [@elastic/eui] depends on [@elastic/datemath] but it's not using the local package. Update its package.json to the expected value below.
 info Additional debugging info:
 │ info actual: "@elastic/datemath": "^5.0.3"
 │      expected: "@elastic/datemath": "5.0.3"
 │      package: @elastic/eui (~/projects/kibana/packages/elastic-eui/package.json)
 │ info actual: "@elastic/eslint-config-kibana": "^0.15.0"                                  │=
 │      expected: "@elastic/eslint-config-kibana": "0.15.0" 
 │      package: @elastic/eui (~/projects/kibana/packages/elastic-eui/package.json)
After fixing those it continues:
ERROR [single_version_dependencies] Multiple version ranges for the same dependency
      were found declared across different package.json files. Please consolidate
      those to match across all package.json files. Different versions for the
      same dependency is not supported.
      If you have questions about this please reach out to the operations team.
      The conflicting dependencies are:
        @babel/core
          ^7.11.6 => kibana, @kbn/dev-utils, @kbn/i18n, @kbn/interpreter, @kbn/optimizer, @kbn/pm, @kbn/ui-framework, x-pack
          ^7.11.4 => @elastic/eui
        @elastic/charts
          23.2.2 => kibana, @kbn/ui-shared-deps
          ^20.0.0 => @elastic/eui
        @types/classnames
          ^2.2.9 => kibana
          ^2.2.10 => @elastic/eui
        @types/jest
          ^26.0.14 => kibana, x-pack
          ^24.0.6 => @elastic/eui
        @types/lodash
          ^4.14.160 => kibana, @elastic/eui
          ^4.14.159 => @kbn/pm, @kbn/telemetry-tools, @kbn/test
        @types/node
          >=10.17.17 <10.20.0 => kibana, @kbn/pm, x-pack
          ^10.17.5 => @elastic/eui
        @types/react
          ^16.9.36 => kibana, x-pack
          ^16.9.34 => @elastic/eui
        @types/react-dom
          ^16.9.8 => kibana, x-pack
          ^16.9.6 => @elastic/eui
        @types/uuid
          ^3.4.4 => kibana, x-pack
          ^8.3.0 => @elastic/eui
        @typescript-eslint/eslint-plugin
          ^3.10.0 => kibana
          ^3.10.1 => @elastic/eui
        @typescript-eslint/parser
          ^3.10.0 => kibana
          ^3.10.1 => @elastic/eui
        axe-core
          ^4.0.2 => kibana
          ^4.0.1 => @elastic/eui
        babel-eslint
          ^10.0.3 => kibana
          ^10.1.0 => @elastic/eui
        babel-jest
          ^26.3.0 => kibana, x-pack
          ^24.1.0 => @elastic/eui
        chai
          3.5.0 => kibana
          ^4.2.0 => @elastic/eui
        chromedriver
          ^87.0.0 => kibana
          ^77.0.0 => @elastic/eui
        classnames
          2.2.6 => kibana, @kbn/ui-framework, x-pack
          ^2.2.6 => @elastic/eui
        enzyme-adapter-react-16
          ^1.15.2 => kibana, x-pack
          ^1.15.3 => @elastic/eui
        enzyme-to-json
          ^3.4.4 => kibana, x-pack
          ^3.5.0 => @elastic/eui
        eslint-plugin-babel
          ^5.3.0 => kibana
          ^5.3.1 => @elastic/eui
        eslint-plugin-import
          ^2.19.1 => kibana
          ^2.22.0 => @elastic/eui
        eslint-plugin-jest
          ^24.0.2 => kibana
          ^23.20.0 => @elastic/eui
        eslint-plugin-jsx-a11y
          ^6.2.3 => kibana
          ^6.3.1 => @elastic/eui
        eslint-plugin-mocha
          ^6.2.2 => kibana
          ^6.3.0 => @elastic/eui
        eslint-plugin-react
          ^7.20.3 => kibana
          ^7.20.6 => @elastic/eui
        eslint-plugin-react-hooks
          ^4.0.4 => kibana
          ^3.0.0 => @elastic/eui
        faker
          1.1.0 => kibana
          ^4.1.0 => @elastic/eui
        geckodriver
          ^1.21.0 => kibana
          ^1.20.0 => @elastic/eui
        jest
          ^26.4.2 => kibana, spec-to-console, x-pack
          ^24.1.0 => @elastic/eui
        jest-cli
          ^26.4.2 => kibana, x-pack
          ^24.1.0 => @elastic/eui
        mocha
          ^7.1.1 => kibana, x-pack
          ^5.0.4 => @elastic/eui
        prettier
          ^2.1.1 => kibana, @kbn/plugin-generator, @kbn/pm, spec-to-console
          ^1.19.1 => @elastic/eui
        prop-types
          ^15.7.2 => kibana, @kbn/i18n, @kbn/ui-framework, x-pack
          ^15.6.0 => @elastic/eui
        react-redux
          ^7.2.0 => kibana, @kbn/ui-framework, x-pack
          ^7.2.1 => @elastic/eui
        sass-lint
          ^1.12.1 => kibana
          ^1.13.1 => @elastic/eui
        typescript
          4.0.2 => kibana, @kbn/ace, @kbn/analytics, @kbn/apm-config-loader, @kbn/config-schema, @kbn/config, @kbn/dev-utils, @kbn/i18n, @kbn/logging, @kbn/monaco, @kbn/plugin-helpers, @kbn/pm, @kbn/release-notes, @kbn/std, @kbn/telemetry-tools, @kbn/utils, app_link_test, core_app_status, core_plugin_a, core_plugin_appleave, core_plugin_b, core_plugin_chromeless, core_plugin_route_timeouts, corePluginStaticAssets, core_provider_plugin, data_search_plugin, docViewPlugin, elasticsearch_client_plugin, index_patterns_test_plugin, kbn_sample_panel_action, kbn_top_nav, kbn_tp_custom_visualizations, management_test_plugin, rendering_plugin, ui_settings_plugin, kbn_tp_run_pipeline, x-pack, alerts
          3.7.2 => @elastic/eui
        core-js
          ^3.6.5 => kibana, @kbn/optimizer, @kbn/ui-framework, @kbn/ui-shared-deps
          ^2.5.1 => @elastic/eui
        glob
          ^7.1.2 => kibana, @kbn/es, @kbn/pm, spec-to-console, @kbn/test, x-pack
          ^7.1.6 => @elastic/eui
        moment
          ^2.24.0 => kibana, @kbn/config, @kbn/dev-utils, @kbn/telemetry-tools, @kbn/ui-framework, @kbn/ui-shared-deps, x-pack
          ^2.27.0 => @elastic/eui
        moment-timezone
          ^0.5.27 => kibana, @kbn/ui-shared-deps, x-pack
          ^0.5.31 => @elastic/eui
        pegjs
          0.10.0 => kibana, @kbn/interpreter
          ^0.10.0 => @elastic/eui
        uuid
          3.3.2 => kibana, @kbn/interpreter, @kbn/ui-framework, x-pack
          ^8.3.0 => @elastic/eui
        autoprefixer
          ^9.8.6 => @elastic/eui
          ^9.7.4 => @kbn/optimizer, x-pack
        babel-loader
          ^8.1.0 => @elastic/eui
          ^8.0.6 => @kbn/interpreter, @kbn/monaco, @kbn/optimizer, @kbn/pm, @kbn/storybook, @kbn/ui-framework, x-pack
        css-loader
          ^4.2.2 => @elastic/eui
          ^3.4.2 => @kbn/interpreter, @kbn/monaco, @kbn/optimizer, @kbn/ui-framework, @kbn/ui-shared-deps
        eslint-import-resolver-webpack
          ^0.12.2 => @elastic/eui
          0.11.1 => @kbn/eslint-import-resolver-kibana
        file-loader
          ^6.1.0 => @elastic/eui
          ^4.2.0 => @kbn/optimizer, @kbn/ui-framework
        get-port
          ^5.1.1 => @elastic/eui
          ^5.0.0 => x-pack
        html
          ^1.0.0 => @elastic/eui
          1.0.0 => @kbn/ui-framework
        node-sass
          ^4.14.1 => @elastic/eui
          ^4.13.1 => @kbn/optimizer, @kbn/ui-framework
        postcss-loader
          ^4.0.1 => @elastic/eui
          ^3.0.0 => @kbn/optimizer, @kbn/ui-framework, x-pack
        raw-loader
          ^4.0.1 => @elastic/eui
          ^3.1.0 => @kbn/ace, @kbn/monaco, @kbn/optimizer, @kbn/ui-framework, x-pack
        react-test-renderer
          ^16.13.1 => @elastic/eui
          ^16.12.0 => x-pack
        resolve
          ^1.17.0 => @elastic/eui
          ^1.7.1 => @kbn/eslint-import-resolver-kibana
        sass-loader
          ^10.0.1 => @elastic/eui
          ^8.0.2 => @kbn/interpreter, @kbn/optimizer, @kbn/ui-framework, x-pack
        style-loader
          ^1.2.1 => @elastic/eui
          ^1.1.3 => @kbn/interpreter, @kbn/optimizer, @kbn/ui-framework
        terser-webpack-plugin
          ^4.1.0 => @elastic/eui
          ^2.1.2 => @kbn/optimizer
        url-loader
          ^4.1.0 => @elastic/eui
          ^2.2.0 => @kbn/interpreter, @kbn/optimizer
        webpack
          ^4.44.1 => @elastic/eui
          ^4.41.5 => @kbn/eslint-import-resolver-kibana, @kbn/interpreter, @kbn/monaco, @kbn/optimizer, @kbn/pm, @kbn/storybook, @kbn/ui-framework, @kbn/ui-shared-deps, x-pack
        webpack-cli
          ^3.3.12 => @elastic/eui
          ^3.3.10 => @kbn/interpreter, @kbn/monaco, @kbn/pm
        webpack-dev-server
          ^3.11.0 => @elastic/eui
          ^3.8.2 => @kbn/ui-framework
        yeoman-generator
          ^4.12.0 => @elastic/eui
          1.1.1 => @kbn/ui-framework
        yo
          ^3.1.1 => @elastic/eui
          2.0.6 => @kbn/ui-framework
        @types/chroma-js
          ^2.0.0 => @elastic/eui
          ^1.4.2 => x-pack
        chroma-js
          ^2.1.0 => @elastic/eui
          ^1.4.1 => x-pack
        react-ace
          ^7.0.5 => @elastic/eui
          ^5.9.0 => @kbn/ui-framework
        react-dropzone
          ^10.2.1 => @elastic/eui
          ^4.2.9 => x-pack
        react-is
          ~16.3.0 => @elastic/eui
          ^16.8.0 => @kbn/babel-preset, @kbn/ui-shared-deps, x-pack
        tabbable
          ^3.0.0 => @elastic/eui
          1.1.3 => @kbn/ui-framework
error Command failed with exit code 1.
info Visit https://yarnpkg.com/en/docs/cli/run for documentation about this command.
Hope you can provide some advice to overcome this.