I understand where you are coming from, but would it really be necessary? From what I see, there aren't any suggestion specific prefix's (since everything is already sorted by sub-section) if they were to add one for sprites it would only be fair to add one for the details. But what if you have both? A third prefix for being both detailed and having sprites?
As Seeker mentioned, the sprite isn't what makes a suggestion. If you create a thread with loads of awesome sprites with no explaination on what they are (stats on items, abilities on enemies, ect.) you don't have a suggestion thread, thats an art thread.
Personally, I think the section is fine without all these extra prefixes, anything in there should be a suggestion and thats what I'm going to look for when visiting the section. If the staff decides to add extra prefixes then thats totally fine. I'm not against the idea, but I am not for it.