I don't disagree that Rust's developer productivity story is still far from mature, especially wrt. async and its ecosystem (and the Rust design team agrees that this is a concern) but if you're going to argue for Vala as a "future design", we should similarly assess Rust's long-term potential. The language is improving quite fast and adding major new features (consider GAT and improvements in const evaluation) despite being quite stable and reliable in other respects. Very different from most "corporate"-focused languages.

(Don't get me wrong, I'm quite fine with also focusing on hobbyist, proof-of-concept languages for potential improvements to developer productivity. But then I'll probably want a Pony.)