What game do you think is doable but has been missed .... ????
I think a Super Mario game like the NES game hasn't been done? Can't think of anything that comes close? Scrolling landscape in which you jump around, etc. I don't see much point in converting Super Mario (NES) to prove it can be done - though for someone to take that on - would be their choice and work to do. I'd prefer to see something that can look different and better? And play better too? It'll take a lot of work - any kind of project - but it could be 1/2 done to show what was always possible ... I don't mind seeing 1/2 done projects - if the source code/etc etc is there for someone else to carry it further along it's development path. Some people don't really care about the credit part - and just like to see some WIP being done... To show this hardware was capable of equalling or better it's competitors.
Wonderboy is of the same type - in a very general sense.
The same can go for a Megaman (NES) style game - while it's like the above but with more shooting present. It sounds like a 2 button joypad is needed - so if a MegaDrive/Genesis controller can be programmed? It'll be the ideal controller for it? Rick Dangerous and Cybernoid could be said to be of this type ... But Megaman is more fun?