Modify Kibana Source Code

My company uses ELK to do business analytics, and we generate millions of documents every day.
One problem we have is that in Kibana reports, we need the legend to have enriched data like user names, product names, sales manager names, product type names etc. In our case, the names are pretty long, we included the names in the index (indexed but not analyzed option). The names are still pretty big and occupies a lot of disk space.
It would be good if we only need the product ID, user ID, type ID (mostly in byte format) in the index to save the hard disk space. And then in Kibana side reports, we do look ups in a csv file and generate list of the names in the legend.
Is this functionality already in your roadmap for the next version?
My company currently is using Kibana 4.5, Elasticsearch 2.3, I want to fork a branch of Kibana and add client side enrichment in the package. If I modify the source code of 4.5 to meet my company needs, then, if later we upgrade to kibana 5 will the same change be applied or there would be significant design change?

To be simple, I want to know shall I modify Kibana 5 and let it work with Elasticsearch 2.3 or shall I modify Kibana 4.5 and then later when my company upgrades to Elasticsearch5 and Kibana5, I can apply similar change conveniently?

Another solution could be to use scripted fields to script the lookup process within the query itself.

Why not add the functions and make a PR to core, it'd be a great feature I am sure many would be grateful for :slight_smile:

to answer your question about the versions:

we prefer all PRs to master branch (currently 5.0) and we then backport important features to old versions. this way we make sure we dont have feature regressions in newest version.