Bradford Welch of 343i today confirmed on his twitter feed that AA’s and classic matchmaking will return for Halo 5: Guardians
On the topic of JiP (join in progress) being only in 4 Bravo has the following to say
This makes me believe that Halo 4 will be the only game to feature the JiP feature, however it hasn’t been discussed apart from keeping CE, 2, and 3 the way they were released. Does this mean that we could see a removal of JiP of Halo 4? More to come soon!