All those changes so far will quite probably affect main page design, especially on wikis, that doesn't use main page columns tags.
Of course it could be tested on real main page on community test wikia, but some users, me included, feel hesitant to play with that page, as they fear their tests could be considered vandalism.
I'd like to have the option to create my "personal" main page (not 100% personal, as other users could still see and edit it), where I could test new features regarding main page. It should have the same width as real main page, have an ad in top right corner (or, if that's impossible, an object that behaves like top-right ad) and mainpage tags should function as normal there.