Heuristics for Development in Erlang

Yes

off the top of my head, for elixir:

cars.com, divvy, pepsico ecommerce, slab, ramp, discord, bleacher report, weedmaps, $DAYJOB, etc.

transport.data.gouv.fr, the transport part of the french open data portal. Source code here: https://github.com/etalab/transport-site/.

Yes, lots of people are, with Elixir/Phoenix being inspired by Ruby/Rails.

I haven't personally done web apps that way, but used Erlang years ago for some non-web TCP servers that handled 1000s of connections without breathing hard. There were a few gotchas that had workarounds then, and that might have real fixes by now.

Erlang's picture for scattering stuff across multiple servers isn't as great as it might at first sound, but it is something. I do think the BEAM's lightweight process model is how all the popular interpreted languages (Python, Ruby, JS) should work by now. Unfortunately we still end up using OS threads and/or messy async schemes instead.

We (Frame.io/Adobe) are all-in on Elixir, and we're hiring!

as well as - Community, BlockFi, Boulevard, Zillion insurance, Pass It Down

They're both dying tech. I personally was a huge fan or Erlang/Elixir but I couldn't take it anymore - there are no jobs and no corporate backing, it's doomed to fail. I finally gave up and moved to Go.