Sweet and short.
Make a player's displayed power level (as they appear to other players) a fraction of their real power level equal to the amount of KI they have left out of their KI maximum.
I'll try to simplify this:
Say your KI is at 50%, so half your bar is colored. When people...
If, and when you feel inclined to change classes after awhile, does your PL from all your *hard* work(haha...), transfer over to your new class? Porportionally of course or whatever, linearly, expontially, blah blah black sheep.
So... does it? Or do you have to start over? Just wondering.