Jdlrobson, the code I provided would allow a different default to be set on each project; if only enwiki wanted full width as a default then no other wikiproject would need to be affected.

Those discussions appear to focus on displaying it regardless of page width, rather than discussing displaying it on pages where it is disabled. On the latter I don't think it is a good idea, as non-functional buttons are likely to confuse users.

Regarding part of ovasileva's comment at VPT, one solution to allow logged out users who had set full width as their preference on Wiki's where limited width remains the default would be:

I might be missing something else obvious here, but I believe that issue could be fixed with the following changes: