More companies will go with I6, and they have a lot of catching up to do with BMW.
Reason is that from cost cutting perspective, I6 makes much more sense since 4 and 3cyl engines could be derived from it (which BMW is doing for years). MB went back to I6, FCA is going that route, Mazda now. Companies like Toyota will borrow engines like they do from BMW as they need V6 for minivans etc.
However, what Mazda is doing is using opportunity. Honda could offer TLX at least with longitudinal engine and RWD. Toyota could make IS more fun (though they did achieve to make RWD vehicle that understeers like FWD vehicle), but they do not. Mazda can only survive if they go bold and where other are not going.