Sony would be crazy to go into MF on it's own. First, you need a SYSTEM for MF, and if one thing Sony has proven, they don't know how to develop a photographic SYSTEM, only products in chopped up segments that are constantly changing.
You need LENSES, and if you're going to do your own mount, you have a lot to overcome. Perhaps they can leverage their relationship with Zeiss to have them re-hash the old Hassy CF lenses into their new mount.
I seriously doubt that those who use MF systems would look seriously on SLT or mirrorless systems, but I don't doubt that Sony would try that and wonder why they're failing.
They could 'cheat' and do a 'mini-MF' system by putting a square FF sensor in a DSLR body, using existing FF lenses, and there would be those who wold buy that. Using existing 24MP densities, that would give you 36MP, and using 36MP sensor densities you would get 54MP.
Give me either in a decent camera and you've made me very happy when I'm doing weddings, as the square format allows you to decide on orientation later via crop!
An a700 and couple of a580s, plus even more lenses.