Please this is 1 major thing I personally hated about Halo Reach and Halo 4.
Looking at Halo 5 and it seems to be going back to a more competitive playstyle.
We most likely will have something along the lines of Ranked and Social.
Now my problem with H4 and HR MM was that if you searched by yourself in say Team Slayer most of the time it would match you up with a Team of 4 while your team is all single people searching solo.
Now MM should work more like Halo 2 and 3 when it comes to matching you up.
Say your searching in a team of 3 then you should be paired with another team of 3 and have the possibility of finding a single person to make a 4v4. Same with say searching BTB when your in a party of say 6-8 you should be looking for another said party in the same size.
When your playing Ranked its not fair to be matched against a team that is partied up and ready to go when you get thrown on a team of people who have never once played together.
Now for social this isnt a big deal because most people play social playlist to relax and not try as hard, plain and simple have fun.