Vetrex
3D vector graphics, bab-ey! I wouldn't expect a straight port here, an interpretation would probably be best. Your character graphics would no doubt get lost amongst a complicated background so simplification is probably required. I love the speed this thing runs at though and am convinced it could work. However, two players? Yeah, sure, why not?!
ColecoVision
A more obvious one but a DD on the ColecoVision would have probably bridged the gap between the 2600 and NES versions. I reckon it could be quite good too.
Neo Geo Pocket Color
Now you're talking! SNK's ace 1999 handheld games had their own unique take on the 'real' things; for example the King of Fighters series uses deformed 'cutesy' like designs instead of a more 'realistic' look (think Gem Fighter). With way too many one on one games to mention, a Double Dragon style game would have been a refreshing change.
Anyone else have any other ideas? Maybe we can try and get a few mock ups to make this more interesting!
Disclaimer - Screenshots shamefully stolen from various sites...
