First of all, I appreciate the effort and I like the idea of limiting the maximum level of cards, but forcing a minimum level is just terrible. It makes sense for survival where it is all about the individual cards, but makes no sense in modern. Have Champ be the elite high spender league where you can only play max cards, fine with me (even though I think 53% of rewards for that is very top heavy), but Gold and Diamond, even Silver with commons having minimum card levels is beyond terrible.
Imagine you are a Gold level player and you can't play your new legendary you got from a pack until you got 2 more? This is madness. I mean, this is discouraging pack sales if you likely end up with cards you can't play anyway in your preferred league. I know I wouldn't buy a single pack anymore. Or reward cards, yay I got a legendary, only 2 more until I can play it, fun. Did I mention this is terrible? Reminds me very much of the old days when you were punished with lower rewards for playing a low level card and were encouraged to go for suboptimal plays instead. This is EVEN WORSE because you don't even have the choice!
What are you even afraid of that makes this necessary? That people play in a "too high" league with their cards and get better rewards than if they would play in a lower league? So what? Let them. A player who can win in diamond with level 1 cards earned it. The winrate should even it out, right? If not the formula is bad, but making players not be able to play their cards is worse.
If you think we will end up with everyone in the champ bracket unless there are minimum levels it just means that everyone is fine with playing vs every level of cards and NOTHING CHANGES. Players have been asking for fairer competition, if the greed wins out (or maybe players enjoy the challenge, have you though about that possiblity?) players will just have to deal with high level decks. It is a decision, do I want to eliminate the risk of decks much stronger than me and have lower rewards or not.
Voting against it and will lobby as much as possible to stop this. This proposal could easily kill modern as a viable format.