This is the thing.
cRPG is sort of meh. Its so imbalanced, hard to actually enjoy the game without jumping straight to lvl 30.
Also, all cRPG has to worry about is importing a skill/items/user profile list from their servers. Its relatively stress free, especially when you do all the work externally. A Co-op/persistent MMO approach means you have to relay the whole lot of new features that an MMO needs to survive, like in-game guilds, pve, pvp, tournaments, global events...etc
The engine alone has troubles handling these kinds of things. They'd have to redesign EVERYTHING while focusing more on making the MMO approach work, as opposed to making what they already have better, more refined and more enjoyable, which is the priority, at least for me that is. They need to get Warband right first before they can jump up in their scales.
While its in an OKAY place in Native, Warband would benefit from some balancing. Not just in stats, I'm talking animations, mechanics, and things like archery.