Pete,
If I had to hazard a guess, I would predict TT have revised the Plug2's circuitry so the PAT cable's effect is integrated into the basic unit. In other words, I would expect The Plug III to produce its maximum output at lower speeds as with the PAT cable of the Plug 2 Plus version...but without the cable attachment.
I do notice SJSC's projected price for The Plug III is the same as for The Plug 2 Plus.
I don't *think* TT could increase the absolute output to a higher base current capacity (say capable of supplying 5vdc @ 1.0A/1000mA), but it will be interesting to see; I hope so!
Best,
Dan. (...whose crystal ball is still foggy)