well, after working on math for kaioken, i've come to the conclusion that goku without kaiken is weaker than vegeta. After some time, he masters it so it's like a constent power increase, like he worked out himself (mastered it so well he no longer suffers the drawback of kaiken, as long as the level of it is within his ability, like x20 became). Thus, i consider him even now using kaioken, to an extent. ;D
As for super kaioken, if it is added, we have several options:
-a melee technique
-a power up
-a ssj only beam attack
and i for one don't really see the need for these. If you wanted to add kaioken, we would have to make goku weaker, so that while kaioken x 20 he would be equivelent to the other characters. So, if you get knocked down, you get extremely weaker, thus making goku a more experienced-player character. Noobs would get slaughtered fighting with him.
my two cents (i'm not as rich as wolfjager):cry: