"Current diff designs do not support this setup. Both in available gear ratios and toughness. But wouldn't this depend on the Kv. of the motor and Volts used?
I am sure the ideal unit could be found to match a good racing speed and the correct torque loading to match diffs capacity."
The outrunner shines in the Torque department. Diff design is advancing. I'm impressed with the New E Revo Diffs. I have put my MT through hell and back over the past two years and I'm only on my second set. LOL
I like one members quote. "I don't use a slipper clutch, I use Tires".
We NEED drivetrain parts tough enough to transfer Explosive Torque Levels of power to the wheels. It's getting there. 
"The lowest toughest gear ratio on the market currently is the 13/43 diff setup. I do know MT tires in the 5.75" size won't work with this without cogging. Perhaps a smaller tire size will. This is what I am wondering myself, but haven't you tried this with pretty good success?"
Yes, with a AXI 4130/20 305kv motor. It did work pretty well, but it did cog some on start up. It needs slightly lower gears. Top Speed was lacking. A good Castle HV Controller would take care of this.
Castle has improved startup routines. They may have practically solved this problem themselves. More testing would answer this question OR a lower kv motor and higher voltage.
The Diff will unload to the front wheels. Yep, just like over powered center diffs do now. Be prepared to stiffen things up.
The MMM works fine with outrunners but limits things to 6S operation.