This would mean a lot less well made ranked insane/extra diffs. Some more hard/easy diffs. Cleaner look when looking at ranked beatmaps, probably more comparable to commercial rhytm games.
I think it'd be better to add some category that's easier to rank for this kind of spreads (one diff per category), but let people do it how it's been done.
Mappers are not working for you, they do it because they want to. This would probably make them less likely to rank a map.
Please use carrot, not stick.
Also, why is this not news on the front page?