I have to say I disagree. I’ll explain why:
First of all, such a thing has been suggested time and time again for both Java and Bedrock.
Second, this so called “famous clean” is nothing more than a strategy. Cleaning is taking advantage of your opponent’s weaknesses (in this case: their HP), yes, but just think about it: other strategies, like getting players close to the edge and hitting them off, or anything else PvP is all a strategy that takes advantage of the opponent’s weaknesses. Therefore, it is not necessary to do anything about it. It is something everyone does, sometimes even unconsciously.
Furthermore, because it is not anything game-breaking, I doubt anything will be done against this. Opponents who clean are unavoidable. Like I said before, everyone has done it at least once or twice, even sometimes without realizing it was cleaning. However, there are countless methods to avoid cleaning when you’re on low HP by, for instance, moving away from the current island or some alternative method. Or eat/gapple up before your other battle ends (or have a potion ready if possible).
I don’t think your suggestion would help at all, because it would cause countless of other issues. For instance, if there’s already a 1v1v1, or else, going on where cleaning is not the case, you could damage one opponent and almost kill them, and damage the other one as much, but they get the final couple hits on them, they would get the HP increase. Everybody should have a chance. Not only the person with the kills. Besides, in such a case, the HP increase shouldn’t even happen, but it’s not like a plugin can detect when a clean happens and when it doesn’t.
Cleaning isn’t game-breaking, but the HP increase would be. That’s why I don’t think it’s a good idea.