> The tooling now revolves around VS Code

When I was there a couple of years ago, doing Hack development using vim was well supported. Not as slick as the official IDE, but more than good enough for my day to day tasks.

> There's literally no reason to justify the massive investment a complete rewrite would be, like literally none. It's not even close.

Definitely, and my (relatively ancient) background is as a PHP-mocking Perl developer.

In the end, the tooling is far, far more important and relevant than the language, and the tooling at Facebook is better than anything I've seen elsewhere, by a long shot.