They ended up being extremely costly choices. Facebook resorted to developing its own language that only Facebook uses to escape from PHP. Dropbox also tried developing a complete new Python runtime because Python is so slow (but they gave up eventually). Dropbox had to rewrite their sync engine in Rust, and I think they also have rewritten backend stuff in Go.
> They ended up being extremely costly choices.
Extremely costly choice would be choosing .Net or Java and never releasing at all. Creating Hack advanced whole PHP ecosystem and cost nothing in the grand scheme of things.
> Dropbox had to rewrite their sync engine in Rust, and I think they also have rewritten backend stuff in Go.
Bah, idiots, should've just waited 4 years until Go and Rust came into existence.