What to put into consideration while adding a new Kibana-5 data source?

I'm attempting to add solr as a new data source for Kibana-5 to read from. Does it all it take is to only add a new plugin to the source code or there are other areas where I should take into consideration?

You make it sound very simple: "only add a new plugin". I think this will be very hard, since Elasticsearch and its query DSL are baked into Kibana very deeply.

Lucidworks tried to fork Kibana twice:

• https://github.com/lucidworks/silk — no commits since February 2016
• https://github.com/lucidworks/banana — no commits since January 2017

You can probably take a look at their commits to get an idea, but this will be a lot of work.