I wish and I'm sure Rust will get there some day but is there a no-brainer usecase today where it's really important to use Rust, one important enough to overlook the initial learning curve, developer scarcity and evolving ecosystem?

If there's a killer open product out there where the primary supported language is Rust(Linux kernel might as well be it someday), or if a big company launches a successful product in Rust then adoption may accelerate. For now its mostly limited to cryptocurrencies, performance critical paths or rewrite of hidden core components but nothing flashy.

"Nobody ever gets fired for buying IBM". Unless teams can say the same about their choice of Rust, people are going to be risk averse and prefer using safest choice as long as its good enough.