I actually have made such suggestion somewhere else but Ting_Thing encouraged us to make a suggestions lately even if he will not respond nor answer something. My suggestion about the custom spritesheets is exactly to make an option to Upload new content for the enemies, items and projectiles which doesn't replace the old ones. Right now uploading new sprites adds a lot of limits and I have to cut out a lot of nice already existing sprites just for creating tricks(triggers) to make a special effects for my game. I am not sure how exactly my whole game will going to be and I am not sure if I really don't need to use any content that I must cut out from the game. Also if someone likes my content and want to use this he/she must consider if it may mess up own game, should he/she should edit my content or to not use this at all. At least PRO should have a way how to upload limitless sprites, especially for the bosses as there are very few for them now.
I am not sure if such suggestion was considered previously but the main reason why I post it again for the official forum also although I have written this previously is that it is one of the important suggestions that I would like to see accepted in the future. This doesn't mean of course that I require something.
Final decision is Ting_Thing's to make and I fully understand this what ever he decides. 
I don't suggest to remove a feature to replace sprites. It is good too for them who want to have some copyright or for them who just want to improve the graphics for their game. Removing a feature to replace sprites I suppose also would remove a way how to add another sprites to special enemies such as wizards and lava monsters. Or if adding some extra settings for the custom enemies and more then it still would be extra work to add everything again.
What I need is however, uploading new and I think it wouldn't be unused also by other people.
