(Firstly, apologies for breaking threading, and not quoting things as fully as I normally would. I only just subscribed to this list, so don't have previous mails in my mail client.)
I'm the main author of the Erudite skin[0], which Daniel Friesen helped a good deal with when shepherding it into the gerrit git system. So consider me biased to prefer the way that skin does everything ;)
I think Bartosz' proposal to clean this stuff up is good and important. In particular, making the official skins use their own directories (and not skinname.php & skinname/*) is nice for several reasons, not the least being to provide a good model for others developing skins to follow.
Bartosz' second proposal, "$IP/skins/SkinName/ for both assets and PHP files" is a good one I think. I agree with Tyler and Bartosz' points regarding the extensions/ vs. skins/ directories; namely that the skins/ directory is a sensible place for skins, and the fact that they in practise aren't fundamentally different to extensions is largely irrelevant.
To Tim Starling's point about making skin installation / upgrading automatable; that shouldn't be much more challenging at all using skins/ if they're in a separate directory to extensions; it can't really be a code reuse issue, unless it's really bad code ;)
To Tyler Romeo's point about how skins are needlessly complex, and a templating system would be much nicer, I don't really agree. Being regular PHP gives a lot of flexibility, and in practise the vast majority of a skin can already be just HTML with <?php tags for inserting the appropriate content. Have a skim of the Erudite code to see what I mean[1]. Granted I'm probably a bit code-blind from having spent a long time with that bit of PHP, but to me it feels really clean and straightforward. I'm sure there is some work that could be done to reduce boilerplate code a bit (as Daniel mentioned), but beyond that I think it's quite a good system.
As for the upper vs lower vs camel case issues, I'd like them to magically go away, but I don't have a good suggestion for that. Well, my suggestion would be lowercase everywhere, but that conflicts with general mediawiki style. So, again, I personally am inclined to generally agree with whatever Daniel says on the issue ;)
Nick
0. https://www.mediawiki.org/wiki/Skin:Erudite 1. https://git.wikimedia.org/blob/mediawiki%2Fskins%2Ferudite/fc5b86835e7b942d7...