fish would be better than bash as a system shell as well. More consistent, for example. However, bash is available and usually preinstalled everywhere, in contrast to fish.
My #Bash" history has > 96k entries (woh, believe it or not; because of this too big number, "xterm" + "screen" always stuck when exitting; but "urxvt" + "tmux" work perfectly thanks to "urxvt" daemon mode.)
Porting this huge history database from my daily "bash" to "fish" is just a nightmare ... :D