MMOs just don't work all that well on consoles. They
can be made, and DCUO was an example of even a subscription model working on PS3, but it'd be more expensive for the developers, and in turn the consumers, as SONY will have to take their cut in order to host the subscription top ups on the PS store. Also, patches will take a helluva lot longer to reach console players, as they have to go through SONY/MS' procedures.
Personally, I don't see it happening at all, and if it does ever come properly to consoles, it'll almost certainly be subscription-based in order to recoup the increased costs. I imagine doing it properly would also entail coding for proper keyboard and mouse support.