Fines and disqualification would maybe not bother some teams as it would be loose change to them, the way to really hurt top teams, I dont know what UEFA would think, is affect there prize funds from Europe, take the Group Match Share away from Utd, City or Chelsea and there left with a very lucrative hole in there finances.
The thing what bothers me, what is the true definition of a weakened team, I bet the Stiffs of the top 4 would do well in the Premier League and to enforce it, rules would need to be in place like what I mentioned before X amount of players from your last league game has to be named in the Cup game.
Another way to do it, would be cut the number of league games over Christmas, just play Boxing Day, with next game after being the 3rd Round Weekend
2014-15 Football Season(Who will be the best North East Team)