This is a good idea and it was had before. The aim before was to create a setting for a system only game. The idea probably came off the back of one of my many systems-need-settings rants. We didn't do it because it wasn't as easy a competition to run as other ideas we had.
I think it is worth doing and using the same game is definitely a good idea if it is a competition because then there is a benchmark. Which one, though? Supers is a bit specific and I think we should probably pick a fantasy one. There are so many generic fantasy free RPGs that could do with a splash of life.
As someone who's been playing with and trying to modify Hi/Lo Heroes lately, I'd like to see the community give it a go with that one. Just to find some cool ideas.
Anyone is welcome to run whatever competition they like! Just call for judges, throw some cash into a kitty (Amazon vouchers have been really good in the past), put some rules together, set an end date and market it like mad!
For me to join in, I have to get all passionate about the idea because running competitions is a lot of effort and by the end of it I have to really concentrate to get everything reviewed. For the 24h compos and CPR that wasn't easy and I really liked those. I'm not passionate about Supers games, so I won't be volunteering.