If you're going to allow 2D it should definately get it's own catagory just to keep things neat. I still wonder if it wouldn't be better to have two sites with totally different advertisers for each. Share3D and Share2D.
Two reasons. 1st, it doesn't take nearly the same amount of time to create 2D as it does 3D and thus 2D will over run 3D content quickly. 2nd, It would help choose which advertisers to pursue for which content site.
Just my thoughts.
It is a miracle that curiosity survives formal education. - Albert Einstein