I have a few ideas, although I doubt 343i would be willing to entertain them.
If you remember Halo: Reach, at the end of the mission called The Package, the spartan Jun was, as I remember, ordered to escort Doctor Halsey. If she survived, then he should’ve survived as well. Perhaps throw him in one of the new Halo games and have him team up with Master Chief?
Another idea is if you recall the legendary ending of Halo: Combat Evolved, Sergeant Johnson was thought to have died on the Halo ring. However, he’s in Halo 2, where a marine asks him how he made it back home. His answer was “it’s classified.” How about him end up in Halo 5 or 6 also and claim his survival is “classified”?
Cortana supposedly “died” on Halo 4. One thing I’ve noticed is Master Chief has never failed a mission until then. He was supposed to get Cortana back to Doctor Halsey to be fixed and was unsuccessful. Any chance the Chief could acquire Cortana and eventually take her back to Halsey to fix?
During the campaign of Halo 4, we’ve learned that the Covenant (or the Elites, at least) had broken the truce with humans. Later on, it shows that they have allied themselves with the Prometheans, but we haven’t received a brief explanation as to why or what the Prometheans had to offer the Covenant. Why not explain in more detail of their motives on Halo 5?
As everybody knows, Combat Evolved: Anniversary was only made to celebrate Halo’s 10 year anniversary. Although this idea had already been dropped, why not remake Halo 2? Halo 2 was one of the best Halo games out. (It also was the game that initialized my official status as a Halo freak!) Every now and then, I have the feeling to replay all the Halos in order. The problem is that the graphics on Halo 2 are very poor. Besides that issue, it was on the original Xbox and unless you have the original one or a regular white 360, you can’t play it.
These are just suggestions that I would love to see in the new Halos. Although the idea of the Forerunners in Halo 4 was an awesome idea, I think the campaign of Halo 4 wasn’t exactly as good as the hype (especially the ending). These ideas would be great for 343i to bring back some originality and (in my opinion) would be an excellent success for 343i. And one other issue. I’ve noticed the pace of Halo 4’s MP seems faster and less realistic than in Halo: Reach. The slower, more realistic pace of Reach should definitely be placed in the others.