I've got to admit that I'm a bit puzzled by questions about mismatched motors. I can see where they are coming from, but practical experience doesn't bear it out in my experience. If the situation was say a HST set with 2 power cars, and the rear one was more powerful, in theory the worst case would be the coaches being pushed off the track, or at least wheelspin from the rear loco? My experience is that the 2 actually work to match one another, with the more powerful one being held back in performance by the lesser one. Even double heading, with 2 different locos, I don't seem to get any problems. A big wheeled pacific, say, with a small wheeled tank loco, and in worse case a 'well thought out' tank with low speed gearing, coupled to a 'toy' express loco, the two work together. As for back emf; my controller is a 70s design from Wireless World, adapting the then new technology of drill speed controllers with back emf and shaped pulse width. Biggest problem I find in general is poor electrical pickup. I add pickup to as many wheels as possible, and rely on solid soldered connections rather than wipers (such as in recent Bachmann dmu bogies to underframe) to give the best possible pickup.
I'm not saying it won't occur, and have no practical experience of DCC, though have fitted a few hundred Zero1 chips in my time. Just my musings and practical experience so far.
Stewart