As others have pointed out, the regex engine is the same so the benefits would trickle downstream. For example, VSCode also uses ripgrep and therefore the rust-lang/regex engine.
ripgrep plugged this gap a long time ago by providing PCRE2 support.
PCRE2 supports only bounded length lookbehinds. It is true, it is not a big improvement to have unbounded ones in rust-lang/regex, but it still feels like something.
Pretty minor IMO. And PCRE2 supports lots of other stuff beside look-behinds.