Shit, I haven't seen this stuff for ages. Great work dude.
Actually, this could be done and playable, but I think this needs to be a single player game. Here's a cool idea: Rather than messing with OpenTibia, I'd take (for example) Unity and use sprites in a top down isometric 3d enviroment. You can even model walls and architecture (which are rather simple in Tibia) and use sprites for everything else - possibilities are endless. Most core mechanics already exist and they just would need to be emulated. Of course lots and lots of sprites and animations would need to be done but you can always start small: with just one outfit and a few monsters for example.
I don't know how much sense it makes but in theory, this could work.