Blocking syscalls are a well defined and well scoped class of problems, sure there are other situations where the flow stops and a keyword can't save you from everything.
Your reasoning is exactly similar to the folks who say “Rust doesn't solve all bugs” because it “just” solve the memory safety ones.
I may be more serious than you think. Having worked on applications in which blocking for multiple seconds on a "non-blocking syscall" or page fault is not okay, I think it would really be nice to be able to statically ensure that doesn't happen.
I'm not disputing that, in the general case I suspect this is going to be undecidable, and that you'd need careful design to carve out a subset of the problem that is statically addressable (akin to what rust did for memory safety, by restricting the expressiveness of the safe subset of the languages).
For blocking syscalls alone there's not that much PL research to do though and we could get the improvement practically for free, that's why I consider them to be different problems (also because I suspect they are much more prevalent given how much I've encountered them, but it could be a bias on my side).
Your reasoning is exactly similar to the folks who say “Rust doesn't solve all bugs” because it “just” solve the memory safety ones.