Meteor was/is a very similar technology. And I did some fairly major projects with it.
Given this, I reject your assertion that Meteor is limited to MongoDB and "toy apps".
It also had some pretty serious performance bottlenecks, especially when observing large tables for changes that need to be synced to subscribing clients.
I agree though, it was a great framework for its day. Auth bootstrapping in particular was absolutely painless.
Roughly: Meteor required too much vertical integration on each part of the stack to survive the strongly changing landscape at the time. On top of that, a lot of the teams focus shifted to Apollo (which at least from a commercial point of view seems to have been a good decision).