I know RabbitMQ is Erlang based product and I have a question, is it possible to develop for example RabbitMQ plugins on Elixir and even more generic question can I develop on Elixir for Erlang? How this is natural or may be opposite crazy idea?
You can call most of the Elixir code in Erlang with ease. Tooling is more of a problem, but there exist tools to integrate Mix into Rebar3 (I do not know what build manager RabbitMQ uses). So you can, but sometimes you may need some footwork to make it work as you want.
The short answer is “yes”, and the longer answer is “the notes are slightly out of date, but you should be able to make it”. The main issue is that the disparate rabbitmq repos were merged into a single one, and the instructions for building plugins don’t quite match up anymore.
Some great references, roughly in chronological order: