Well, one could certainly make a massive patch that removed the tuna GUI files and inserted the pianofish files. Then you'd just need to modify the tuna commandline to launch pianofish. Or, rename pianofish so it would become the tuna GUI. It's actually completely independent of tuna, but they could still be packaged together.
I'm retired and don't spend any time on pianofish or any other programming lately, but I would be willing to do some work on it or turn it over to someone else. First though, I'd like to have someone try it out and see if they think it's worth the effort.
--Guy