It's not that I don't like the idea, but this can give rises to unwanted toxicity from players who now can give excuse when they lose: "Oh, I'm just farming coins, you would lose to me at my full power", or go full toxic when they win: "Haha, lost to 5 PU Mon, how trashy are you." It's unnecessary to give extra benefits to someone for playing low tier mon just because they are bored of the current meta.