I think people are missing a lot of new incentives a system like the proposed could bring. Not only would the reduced workload enable experienced mappers make 4-4:59 songs avaible to a broader playerbase (since instead of one topdiff+R3 or the map not being ranked at all, the spread would actually be directed towards a 4 and 5* playerbase). 4 min hard or normal only spreads would be a great opportunity for new mappers to get their first map ranked more easily. That's great, since new mappers are most often mapping to share their own taste in music - thus broadening the ground of genres/artists being playable in the game.
So not only would 4-4:59 songs finally be mappable/playable for experienced mappers/players - also the mapping community could potentially grow more easily in terms of numbers in mappers and artists being ranked.
One downside I could see would be that a lot of fresh music/artists new players search for wouldn't be immediately playable for them - but apart from that being some motivation to become better, I think you could nudge new players into playing appropriately difficult maps by well placed highlighted sets or some algorithm to suggest maps based on their previous plays.
TL;DR: Total number of maps would increase, as well as the growth rate of the mapping community, since it'd be easier accessible for new mappers. New artists/genres would be mapped by new people trying to get their music into the game - often with hard or normal diffs (since easier rankable). New players will more likely find ranked songs they're looking for.
So not only would 4-4:59 songs finally be mappable/playable for experienced mappers/players - also the mapping community could potentially grow more easily in terms of numbers in mappers and artists being ranked.
One downside I could see would be that a lot of fresh music/artists new players search for wouldn't be immediately playable for them - but apart from that being some motivation to become better, I think you could nudge new players into playing appropriately difficult maps by well placed highlighted sets or some algorithm to suggest maps based on their previous plays.
TL;DR: Total number of maps would increase, as well as the growth rate of the mapping community, since it'd be easier accessible for new mappers. New artists/genres would be mapped by new people trying to get their music into the game - often with hard or normal diffs (since easier rankable). New players will more likely find ranked songs they're looking for.