I like this idea of Ki burn for when higher level transformations are made. But there is some problems I can see...
SSJ3 Goku was versing Fat Buu in the cartoon and was only a bit betterthan Buu. This is buu's first form in the show. The last form of Buu (Kid Buu, and even the form before it Super Buu?) would kik SSJ3 Goku's arse. I guess I leave this up to the game team to balance.
But yes, SSJ2 and SSJ3 levels should have Ki burn until certain PLs are reached, because these levels of power were often used in highly intense and emotional situations and would last for brief periods. So you major advantages at these levels would be the immense increase in speed and power level, but your ki pool would burn out quite rapidly compared to lower levels of SSJ.
I only have one questions for you mastasurf, how do you intend to simulate this strain while in SSJ3? Will it be something like: PL 15 million, ascend to SSJ3 - PL jump to 30 million, PL counts down at some rate defined by the PL you ascended at, when the lowest power level for SSJ3 is met you auto-descend to SSJ2, or even to normal form?
I figure there must be some forced descention at some point, unless you have an insanely high PL that allows you to have SSJ3 constantly. (And to have no social life)