A potential future multiplayer model

I've been considering future games I might take on when I'm done with what I have on my plate now and I've had an interesting thought I would like to share. The idea would be to create a multiplayer system that's modular in that it's essentially it's own game and yet can be readily configured for other games and add ons not conceived of at time of launch. Basically rather than launching multiplayer as a tie in have it as a stand alone and treat what would have been multiplayer for a game as dlc for this multiplayer system. People who buy the campaign get free access to it's multiplayer and those that aren't interested can simply buy the add on at reduced cost.

To clarify I mean each and every subsequent game I might put out that might have a multiplayer component would be added to this system or framework to essentially keep it alive indefinitely or at least as long as possible. With regular updates of all kinds to all sections and while each add on would function independently there could also potentially be some crossover or hybrid modes where you could load items and features from different add ons and use them to create a new mode. These modes could be shared and featured and it would really be just an interesting concept if it could work. Granted a lot of things are not so simple it's not like you can load any old code and expect it to work but it's not unreasonable if it's put into consideration to begin with to plan for it as an option. While some multiplayer might be wildly different it's not to say some features couldn't be designated as reusable elsewhere.

Consider the different tiers of the multiplayer in the main game I've been discussing for some time. Each one could effectively function as it's own multiplayer as the difference between tier one and tier four is like the difference between COD and Halo though I wouldn't jump to compare either directly with what I'm suggesting. The concept I present would be like grabbing the plasma grenades and shields from halo and them patching them into COD or grabbing the weapons and accessories for them from COD and throwing them in Halo, maybe grabbing the control scheme or cover system from Gears of War. Consider each different part of each game and consider how it might be used elsewhere. On top of which would be the maps all of which I would imagine to be relatively easy to port over from anywhere to anywhere.

With the potential to basically assemble the perfect multiplayer you ever wanted what would you put together? Comment saying what features you'd put together and why.