It does seem like a good idea, the only alternative for things like skins to be noticed is if they get on the "What's hot" page. Otherwise you're right in saying that they will only be seen on "recently added" and that would be it. I think the main thing that would have to be decided on would be what counts as "popular" - would a popular upload be one that has the most views, or would the number of diamonds, downloads and favourites be accounted for as well, as they can also indicate quality of work, and if so, how would their smaller numbers be accounted for?
If "popular" can be made to account for other factors as well as number of views, it would be a pretty good collection of lists to add to help people get good work noticed over a week or a month.
Really good idea though, I hope it can be added.