I think I understand your concern as the foundation is arguably old. But as someone actively following Erlang and Elixir the sentiment feels absurd. Elixir is very recent, very modern and Erlang/OTP has a very strong track record.
There are drawbacks of course but having worked with Python, PHP and JS. I haven't seen any real drawbacks. I wouldn't choose it for minimal overhead or the fastest compute maybe..
Are you "following" or are you actually using it in production for a real service ?
I'm asking, because to my knowledge, the only "huge number of users" recent success story is whatsapp, and after having viewed all the talks about their stack and experience, it seems that the team was so extremely talented that they probably would have made something good with any tech.
Discord uses Elixir heavily. But if you are scaling to 10s of millions of concurrent users, you're going to need those types of skills no matter the language.
I'm not using it in huge scale. But I've worked with companies that run it in production, yes.
There are a lot of Elixir products and systems out there and before those there were quite a few in Erlang. I don't have a sufficient sample size from my own experience but it is hardly old and disused or too new to be sure.
Changelog podcast runs on it. Dockyard build with it. It seems the new default for many previously Rails shops.
There are drawbacks of course but having worked with Python, PHP and JS. I haven't seen any real drawbacks. I wouldn't choose it for minimal overhead or the fastest compute maybe..
Edit: typo