Sounds like a good idea especially as there seems to be a lot of inspired graphic set creators recently. I've known of quite a few people who have benefited from my Graphic Set Tool tutorial on my channel.
Plus I think new tilesets have been kind of underappreciated on here as of late.
I suppose an obvious criteria is any graphic set which has been formally released on the forums such that people can download it is automatically excluded and it is only allowed for newer tilesets.
Personally I think you're the perfect host for this type of contest GigaLem since I'm always blown away by your artistic creations
I think the trophies is a terrific idea and great touch as well, it would encourage more entries because then it wouldn't be a case of the best skilled graphic set creator just winning the best tileset which would happen if it's set up like the standard level design contests.
Some drawbacks I see are:
1. Tilesets are not exactly as straightforward to create as levels so we'd need a very long submission period, at least double that of level design contests
perhaps a vital topic of discussion here2. This probably wouldn't be able to be hosted in the Level Design Contest forum because it's not a level design contest. But I think it would fit nicely in the Graphic Sets forum.
3. How would the voting work in this especially considering there are so many trophies?
Those are just a few things which come to mind, but I'm definitely for this idea. I would like to encourage more new tilesets from the community on top of the great selection we already have.
If you are short of tileset ideas, Wafflem posted a lot of ideas he had somewhere on here but I don't know where so I think someone else may be able to link it.