As a Gutenberg fan, I welcome such improvements, even if it means I have to refactor some custom code. Mostly it's for the better, and how many popular page builders are held back and unable to utilize modern techniques as css grid or custom properties due to backwards compatibility? It's not much fun.

But forgive me for the maybe stupid question. But could Gutenberg not just let the old gallery block be as is, and create a new "modern gallery" block, maybe offering that as default when inserting? It can't be that much legacy code. Out of date blocks could even be moved to a plugin during transition? Like the classic editor? I could do without the spacer block - that's for sure. :)