I played lots of MWO in its early days and I enjoyed it quite a bit for a good while. However, over time my faith in PGI kinda went and well... while I have goods memories, I'll honestly be happy if they lose the license and someone will then hopefully pick it up and give it a new try. Might be a while though as MW5 is breathing new life into the corpse (and will unfortunately delay what could be another online MW game).
I do think early on World of Tanks was an albatross on MWO's neck, as the latter came out after the first and probably influenced it negatively.
Any new MW game will have the difficulty of appeasing all the game's old fans (in any of its old iterations), while trying to innovative and move on to better things. Some change is definitely needed and that will probably require some bold choices, which may tick off segments of the population used to the old mechanics.
I'd like to see more emphasis on 'Mech movement/abilities beyond being a just glorified tank. So yeah, more agility and movement. Physical attacks and options. Destructible terrain/buildings obviously (well, seems we have that in MW5 already). A factional meta-game that is actually compelling (and maybe has a seriously constrained focus, ie. not the whole galaxy). Perhaps narrow the era down more tightly and differently (ie. just say no to Clans, or move boldly head and embrace higher tech full on, but don't try to be all things to all people). I think the tighter focus/era is what could really do the trick and open up options for innovation. Hell base the whole game on the Clans, with the meta-game being Trials etc. Or just go full tilt with a Solaris game. Something different though.
I definitely don't think PGI is the company to do the renovation though.
But I do miss an online MW game which I'd be stoked to play. :(