Yes a 215 would be great but way overkill for me. Plus portability goes way down when you switch to 15s over 12s.
Maybe I should just make the 12/6 and add a sub later if it's needed... but then I need an 18sound mid and they aren't available here. I wish the the eminence 3012 and alpha6 worked with a sub.
Maybe this is silly but why is the 18sound necessary when a sub is added?
Because it has the needed sensitivity to keep up with two 3012LFs, unlike most 6.5" mid drivers. If it were me I would probably just build one 12/6 with the Alpha driver and build another one later if needed.
IMHO the best option for a pair of 12" fEARful cabs is two 12/6's with alphas.