Generally, fan games are real thrown-together, but from the way the youtube videos make it look, the engine you've created seems really tight and well-programmed. Gotta say, you're probably just going to get a lot of cease and desist notices if you upload this anywhere. May wanna keep a personal copy with the fangame graphics and turn this into a 'mario clone' instead of a Mario fan game before final release. As long as you've got all the programming done, it's generally pretty easy to find somebody to help you with graphics if need be. Pixel artists are only hesitant to help when a game isn't near to done and likely will never see a release.
ChrisD> Employer: Say, wanna see a magic trick?
ChrisD> Employee: Uhh… sure, boss.
ChrisD> Employer: Your job! It just disappeared! Pack your things and leave! Pretty good trick, huh?