Throwback
Smash Lord
The alternative is that players of more mains (7v5) are forced to play a secondary AND they suffer a 1 round defecit from being forced to play the impossible match-up.This rule isn't going to make your players happy at all. Someone who's forced to play a secondary because of this rule will be (rightfully, in my opinion) pissed. It'd be much more reasonable to allow the bunny to repick; that way you're only allowing someone the chance to use a secondary, not forcing them. Even that, though, I'm extremely hesitant to recommend: it essentially lets you counterpick on the first match.
I explored the idea of the bunny repicking when I first drafted this rule, like you said it's not a great idea.
edit @ ZoSo: If you ban infinites do you ban pika's d-throw chain on fox, which isn't an infinite but guarantees a win anyway? What about the wario CG on DK (and apparently bowser). What happens if I accidently d-throw twice in a row with D3 - do I immediately lose the round? You can make specific in-match rules or you can bypass the issue altogether, which is what the IMR does. I'd rather bypass the issue for simplicity, others prefer to ban the specific things they see as broken.