Looks like the major syntax quirk just went away:

> fish’s command substitution syntax has been extended: $(cmd) now has the same meaning as (cmd)

I never really understood the appeal of maintaining perfect bash compatibility in your prompt. The only time I've ever needed that was because I'm copy/pasting something from the internet, which I probably shouldn't be doing at all, and at the very least not with such frequency that it effects my decision of which shell to use.