It would be very cool if there was a playlist for H2, a playlist for H3, and one for reach. Or maybe even 1 playlist that had all of them.
And I am not saying it would need to be updated with H4 game play. Keep it the same as the original. Then everyone who is still stuck on H3 or whatever could simply keep play H4 multiplayer and just choose that playlist. I just look at games like WoW who allow me to continue to keep playing old content even though new stuff is added in and I really like that. On the other hand I hate CoD which forces me to keep switching multiplayer each year when I get so much invested into my stats and such.