You know what would be a huge game changer? The power to change your Spartan. And by this I mean choosing between a
Spartan II, Spartan III, and Spartan IV. Loyal halo 1, 2, 3, fans would mostly likely choose spartan 2's. Loyal Reach fans (me, thou I love halo 3) would choose spartan 3's. And for those who are new to halo and love halo 4 would probably chose spartan IV's. Basically, doing this; everyone gets what they want. I was just thinking about it. Highly doubt something like this could or would happen.
2. Halo 4 multiplayer is too repetitive and basically the same thing over and over. (except griffball) One thing they completely shit on is in removing elites from MP. In Reach if I was a little tired in slayer and always killing Spartans (which surprisingly gets boring after a while) I can switch too Invasion or Elite slayer to experience that awesome Sangehili action!
Even if it isn't customizable like in halo 3, it would really be great if they brought the elites back into the multiplayer.
Bringing the elites back is an idea I definitely agree with, I loved invasion in Reach it was and still is in fact my favourite gametype in that game. I would also love to see the Spartan changing idea, but taking into account the fact that the IVs are faster than the other classes, IIs are stronger than IIIs, I think its safe to say that an equal balance wouldn't be found to make it work.