I keep asking for this but one issue at the moment for ODST Firefight is in the original version (which is why it will take some time to get this working properly), there is no way to specify when a Firefight match will end (or the length of it), it was just assumed when all your lives are gone, then the match will end. the main issue here is it can go on forever, with no end to the firefight match, so a trigger to end the match at like 1 set complete (like it is currently with Reach Firefight) is needed (we need more options to change around in ODST, if not well then specify in matchmaking when to end). The only things you can change around in the lobby before you start a Firefight match is the difficulty and 4 silver skulls.
Also for Spartan Ops right now, I believe this should get matchmaking support as well because that already is built with each mission having an end compared to ODST (with each mission takes about 10-20 minutes in a team of 4, maybe less so its a good length for a matchmaking experience) and you can just play each mission at random like a firefight mission (so if you want to experience the story of the spartan ops from episode 1-10, you can go in solo by yourself or with your own coop team and play them in order like it is right now, like a very long campaign, its not a very good campaign story wise but its part of the lore). And you could get XP after each mission you play like with Reach Firefight! Reach Firefight is going to get boring to only playing that after a while pretty soon and we need more content from other games to fill out this mode to keep it interesting!
Honestly having Reach, ODST and Spartan Ops in the same Firefight menu would totally fill out the content for good in this menu (as there isn't anymore content left to add in anyways after this if this will be the final amount of legacy content for us to play). When 343 gets to Halo 4, they should move the Spartan Ops menu out of the campaign section and move it to the Firefight section since it will be better suited there.