As a brand new player of MxO, but an ancient MMO'er (I started with UO back in 199
I would have to say that there are three main things that could help revive MxO.
For starters, the learning curve in MxO is atrocious. I've played alot of games and there were several aspects of the game that just didn't make alot of sense to me, or that I didn't understand until I went trolling in the forums for guides. You're average gamer isn't going to do that and fans of the Matrix who've never gamed before probably won't either. They'll see something they don't understand and write the game off in the free month. I'd recommend expanding the tutorial a bit and helping the player along for a few more levels. (The game is on an old Evercrack treadmill design as well, so it seems to take ridiculous amounts of time to get to level 50, no suprise that it ended up in SOE's lap, but I digress)
Secondly, this game will never be huge, not by UO or Everquest and certainly not by WoW standards. HOWEVER, that doesn't mean it can't be successful. I have been exceedingly impressed by the amount of RP going on in MxO, of all the games I've been a part of over the last decade, the only one to top what I've seen thus far in MxO is UO. They should try to take advantage of that. For relatively cheap, they could webvertise in alot of places where fans of the Matrix like to troll, but since most of them have already played, they're going to need a gimmick... on to that.
The game needs a code push. Since they are working with devs who didn't design the engine and there appear to be limitations to what they can and can't do in a timely fashion, they need to find a solution to this problem. Whether it be port the game over to another engine (time consuming, anyone?) or hire on some new help temporarily and make a major overhaul to the game (expensive), they need to come up with some persistant, long term goals for players at the end game and be looking into expanding levels/abilities of players. I would personally like to see combat changed as well. Interlock provides some very cool visuals, but the "awe" of those last about 5 minutes after you've seen them. I would say, throw IL out the window and come up with a system for engaging multiple targets in Melee combat simoultaneously (much more Matrix-esque) and allowing the use of other fighting styles against multiple targets. (Shotgun spreads, covering fire from rifles, etc)...
Once they've got their gimmick, they hit the ex-players and Matrix fans who may have never played with a net only ad campaign, maybe even hit some general MMO sites to try and draw people in while at the same time holding onto the people they aleady have with this same new content.