I think the main issue outside of funds and whether or not it would be a good use of resources is whether or not they should as the problem with 4's story is that it felt like they didn't care and if they aren't gonna care than they shouldn't do another one at this point.
I'm not saying game-play doesn't matter I just feel at this point, you are invested in the continuing adventures of these characters and if they aren't gonna make a effort in tying things together or advancing characters, than dont bother.