Are Rust or Elixir still the got to's for dependability or should Go get a look in. Bonus points for good web tooling outside of an API back end.
* https://elixir-lang.org/blog/2021/07/29/bootstraping-a-multi...
* https://github.com/njwest/Awesome-Elixir-Gaming
* https://www.erlang-factory.com/upload/presentations/395/Erla...
* Erlang Factory SF 2015 - Jamie Winsor -Building And Releasing A Massively Multiplayer Online Game https://www.youtube.com/watch?v=_i6n-eWiVn4&t=1131s
* Petri Kero | Building a Scalable, Distributed Backend for Mobile Games - https://www.youtube.com/watch?v=nCSO8yeR0c4
All that being said, Go and Rust are hands down faster and there's no denying that.
Elixir (& the underlying Erlang) and Go certainly come with a lot of concurrency support out of box, and are well known for building websites. Though I imagine Go is usually typically treated as an API backend paired with an SPA like React.
Elixir/Phoenix offers LiveView which makes it easier to skip the API/SPA paradigm to some degree. But the higher the demand on browser interaction, the more you'll probably end up bringing in Javascript to the mix. Though you could use something like https://github.com/woutdp/live_svelte to integrate svelte & liveview.
I'm a huge fan of Elixir/Phoenix myself.
I would almost certainly use whatever stack made my dev team most efficient and if demand was there use resource scaling to bridge the product until we did a rewrite.