Using Wikipedia is a learning process; this cannot be avoided. Implementing subpages properly instead of merely tolerating them makes learning where and where not to use them easier.
I don't agree. We aren't talking about the wisdom of subpages, we are talking about the typing shortcut and the linkbacks. Both are not very useful.
If you wanted to add a warning to regular pages, saying "Uh, it is best not to use the slash character '/' in article titles" with a link to a discussion of subpages, while not having the warning in special pages, that'd be fine with me.
It would be fine with me if we put that message everywhere, saying that we discourage the use of subpages generally.
But we really should discourage them generally by not "supporting" them with useless cute features.
--Jimbo