I guess companies that use Discourse and have huge traffic can pay a bit more, nothing wrong with that.
The point being that said numbers aren't big traffic, they should be handled by a Raspi.
But for the sake of argument: Discourse is a painless move upwards for big budget and/or big knowledge entities. Nothing wrong with that.
On the other hand Discourse isn't a replacement for low cost, decentralized, easy to deploy, engine-diverse, low knowledge communities which were served by a multitude of PHP solutions in the past.
There's an economic argument for a growing divide between "communities as a service" ala Facebook and high hurdle deployments ala Discourse, but one doesn't have to be happy about this development.
Much like Wordpress and phpMyAdmin, these projects are basically victims of their own success.
I don't see how. The repository seems to be quite active and has plenty of current pull requests.
I don't doubt that Discourse requires more resources than most PHP forum packages do, but it doesn't need that much more.
Two thoughts and personal observations on that:
1. Nobody was ever fired for buying IBM. In my impression it's usually deployed as default for and esp. by very tech affine communities. It was the new, hot - and is now save - thing in town.
2. You see postings boasting how the Discourse forum is now powered by a new six core 8 GB RAM server improving performance ... for 200 concurrent active users and 80k posts. Yes, Discourse offers a lot of flashy features, but that's just borderline disgusting.