I'm somewhat surprised that they haven't even announced any information about Mount and Blade 2.
Mount and Blade 2 didn't even show at Paradox's media event, but War of the Roses did. Therefore, I'm assuming:
1.) New engine
2.) War of the Roses will be released before Mount and Blade 2, and there will be a significant gap between both releases. It wouldn't make sense to release two games that are similar in game mechanics so close together, since most people would likely buy one or the other.
War of the Roses will never be Mount and Blade, and in fact, they are more different than in name or developer. War of the Roses is striving to be the CoD/Battlefield of medieval combat. Therefore, combat will likely be slower and easier to cater to the more casual gamers. Also, there is no way that WotR will be getting very many mods. Mount and Blade has always been about the sandbox experience, and when Warband came out, about the epic battles with fast paced combat that (more or less) required a bit of skill. I'd expect Taleworlds to make the sandbox single player even better, hopefully by increasing immersion. (That was a good fight.) Lastly, there is no way that MB2 will lose it's modability.