The goal will be to take benefits of the elixir/OTP platform and the concurrency assets.
Today we have a lot of asynchronous/background task distributed with rabbitMQ. If our investment provide better stack and simplify the architecture , this could be a better ROI than keep the current stack up-to-date.
But if you are migrating just to avoid spending a couple of days learning and migrating to Python 3 based on reading too much FUD I'm very saddened. Migrating from Python 2 to Python 3 is not much harder to handle than a Django migration. Though of course it depends on your codebase, but compared to moving to Elixir/Phoenix/Ecto it's a peace of cake.
Move to Elixir/Phoenix/Ecto because it fits your needs better than Python, be proud of it even. But please, learning Python 3 to write good Python 3 code coming from Python 2.7 is very easy, nothing like switching to a completely different paradigm...