In practice, it fits very well, but I have no problem with it being
an option which you have to turn on explicitly. But it would be
nice to mention it on the splash screen.
Also, if shift-select is implemented as default, I think many users
will be utterly confused if C-x doesn't do cut and C-c doesn't copy.
So all-in-all I really don't see why everybody is making a lot of
fuzz over making shift-select a 1st class emacs feature -- when
we could just as well just leave it to CUA mode to DTRT, but possibly
make a few enhancements to basic Emacs functionalities to assist CUA
mode to do its work.
But once again, I know this is a lost battle...