I refer to this blog post Evolution of Workplace Search: Search your private data with Elasticsearch | Elastic Blog
So it seems the Workplace Search concept is being removed/replaced - but it isn't clear to me whether the interface will remain - going forward are customers expected to build their own interfaces using components?
Yes we will expect customers to build and maintain their own API / UI for workplace search.
We provide boilerplate code for you to use and adapt for your own needs here
You can also use Search UI with the elasticsearch connector, which provides components like SearchBox and Facet so its simple to build your own UI. Quick start here