I'm guessing the auto-complete handling means they need to understand the line editing of the shell. If they've done it well, it'd hopefully be possible to quickly handle others and/or make it configurable.

Ah, that.. almost makes sense? fish at least has its own autocomplete.

I'd be more careful about the messaging then, something like "you can use any shell you want, we provide enhanced features for bash/zsh/fish and are looking to expand that in future".

This. Also the mention of ‘collaboration’ and ‘cloud’ put me off. “Do one thing and do it well”.