Can't say much about async, since I really lack the experience to say whether async in Rust could feasibly and realistically be much better than it currently is. Some people say that it'd be great if it worked as effortlessly as in Go, but I assume that you don't get to have that without performance tradeoffs.

As for lifetimes, what's the issue? Do you have any reason to believe lifetimes are frustrating because they were badly designed, rather than the fact that they're making complexity explicit which was previously hidden?

async, yeah it could be better, given the pains. However note that adding async to .NET and C++ hasn't been a panacea either, to the point that there is a prototype of adding Go/Java green threading to .NET, done by the .NET team. While with the C++ standard library there isn't an executor runtime in the box.

Lifetimes are painful, and a other languages are exploring better ergonomics or combining automatic memory management with affine/linear types, yet it was Rust's adoption that pushed other language designers to actually look into this. So from that point of view, quite a success, even if Rust vanishes tomorrow.