A lot has been said about how Plan9 is "Unix with all the design issues fixed", but as much as I like the idea of "everything is really, really a file", I'm not sure whether I could get used to the Xerox Star style GUI (which you can't easily replace, since it too is exposed to the filesystem), or trade my lovely Vim in for Acme.
GUI (which you can't easily replace, since it too is exposed to the
filesystem)
What? The graphics system is quite nice, there's no reason to replace
that. I'm pretty sure there is nothing tying the graphics protocol to
their GUI paradigm. I think it would be entirely possible to implement,
say, GTK over it.
Vim
There's no reason it couldn't be ported. I would use it if you made it.
It would be nice to have a libdraw based vi, even just in plan9port.
There are several parts, links are on the bottom of each chapter.