Everybody browsing with ?style=mine will still get BML/site-branded comment/reply pages, if your style uses S1/BML.
We'll actually use BML for the frame, not fake it, so we don't need submissions of S2 styles that look like xcolibur/lynx/dystopia/etc... but the inside of the page will be S2, thus solving our duplicate code problem. And over time if/when we get new BML themes, we get 'em for free, and don't have to write S2 for them.
(so the BML pages end up being like 20 lines of code, just to invoke the correct S2 entry point....)
Cool? Cool.