While it is true that the xlabs project is still unofficially accessible, given that it won't be receiving any security or quality of life patches moving forward, it would be appreciated if the plutonium project integrated Modern Warfare II.
It is unlikely that doing so would bring about the same legal repercussions xlabs faced, as plutonium does not currently illegally distribute copyrighted game files.
I imagine that a lot of the heavy lifting this would involve has already been figured out, given that the two games released immediately before and after Modern Warfare II (WaW and BO1) have both been integrated into plutonium.
Alongside Black Ops II, Modern Warfare II is widely considered to be the greatest Call of Duty multiplayer experience of all time.