Non-lock up Torque converters have no mechanical connection from engine to drive train. Everything is passed through the fluid used...in this case, engine oil.
This slippage caused few problems, other than the need for extra cooling, since this slippage is essentially turning mechanical energy into heat energy via viscus friction. In most cases like acceleration, its actually beneficial...
However, one of the problems it does cause is reduced efficiency, for obvious reasons. Because of this, engineers got the bright ideal of adding a clutch inside of the converter, applied via hydraulic pressure when needed. These came into widespread use during the late 70's...likely due to the first oil embargo.
The Pioneer has no such device in its torque converter, so unless you're an engineer with large amounts of machine equipment at you're disposal ( and don't forget electronics to make it work ), there would be no way to add one.
Moose mentioned stall speed, and different design factors go into that. One old drag racing trick is to fine tune the converter's stall and flash RPM by changing to ATF with different viscosity, with thicker ATF dropping those RPM by a small amount, or vice-versa.
This is the reason i always advise against using thicker than stock oil in these machines, since they have been known to bog at times. Don't know if there would be a big enough change in RPM to make a difference on a Pioneer, but it sure seems like a lot of the power complaints come from guys with thicker oils. If anything, the Pioneer could use a higher stall converter.
And that leads me to another thought: Would aftermarket companies make higher RPM stall converters for the Pioneer?
This would have the same effect as clutching mods on a CVT machine for big tires, raising the RPM and allowing the Pioneer to get further into its torque range before really starting to transfer power ( and the tradeoff of running higher RPM everywhere ). For certain people like hardcore mudders, this would be a godsend.
I really expected this when the Rincon came out, but it never did happen. The Big Red didn't sell well enough for it. Now that the Pioneer seems to be selling like crazy, maybe someone will do it, since i would guess that they all use the same TC. Cost would be a factor, as would getting the PGM-FI not to get angry with seeing higher RPM at a given speed.
Just some thoughts, out loud...