It also runs in the browser, no more Java, you could play in the browser without downloading anything. I was thinking why not remake OB2D in this engine?

It could be almost as simple as switching animations and images (well it's probably more, but it can't be that much).
There is also a fully functional single player, allowing new players to learn the game easier. I'm almost positive I will do it, now it's just a matter of finding the time.

A realistic estimate of this would be one month or even less! I think it's worth doing.

Retro is a bit different in that you can select a strategy before the fight (speed, power, endurance, stamina) but so what? No one said OB could never evolve. Moves and everything else would stay the same though.