Okay to give you a great idea of what I mean by a full scale 3D Double Dragon, I will post a few videos to help.
First I will start with Sleeping Dogs:
https://www.youtube.com/watch?v=2ZXSKL7vzQoThis is the fighting tournament section that you can participate as a bonus in the game. From this you can see how the system works with multiple enemies.
https://www.youtube.com/watch?v=XG-abIfiATMIn this video, around the 1:30 mark you can see the fighting, counters, and environmental attacks you can use in the game. Like I said, for a full scale 3D I think if properly done right this would be good in both single and online multiplayer.
Now for Shemue
Shenmue is an older game that had a great 3D fight and feel with vibrant characters. In this scene is the 70 man brawl. While the game is one player, Ryo has an assistant helping him. Like I said, with a full scale online Double Dragon game if done perfectly, this would be amazing.
https://www.youtube.com/watch?v=yCF7lTrD8Mc Now keep in mind that these games aren't pure beat em ups. Sleeping Dogs is a sandbox game like GTA but places a huge emphasis on Martial Arts elements. Shenmue is more linear, but is half beat em up/half RPG. Still, If your talking 3D Double Dragon would have to go deeper into it's system. The story must be properly developed more as well as the beat em up system but as you can see in these two games, the look and feel is possible to make a great Double Dragon game. Double Dragon has the signature characters and you can make the first Double Dragon one story deeper if built in a new format. Some changes would have to be made, but you can actually create the events from the original Double Dragon story especially the Nintendo version.
2D will always be great, but if done in 3D they need to take this route and not the route of DD Neon and Wander. The only problem we had with 2D/2.5D versions are developers making sloppy concepts like DD Neon and Wanderer.