In Johns case the swap over wasn't as severe as everyone is making out and was perfectly within the rules.
In his case, the new drive motor's were failing (not due to opponents) and he needed to swap the drive. Normally it would be seen as being fine if different motors and ESC were swapped out to solve the issue. However roboteer's wouldn't lend their spare motor's and the only other option was to use the other chassis with motors welded in. The previous chassis was no different (other than material but weight was the same) and the first chassis wasn't damaged. This meant the only change in performance was effectively just the drive motors and ESC to suit the new motors.

So in this case I think all the ill comments on this are unjust.

However, I don't think it should be allowed for future competitions to be allowed to change say more than 50% of the robot at any one time to avoid swapping out entire chassis's once the first one was smashed giving them a huge advantage.