Or perhaps it is the other way around. They make these concepts. introduce a bunch of them in the books, and then in the game.
To me, it looks like 343i is keeping tighter rein over various Halo things, trying to fit them together better than before (no comment on retcons like Dawn's looks).
Visual "rectons" are a necessary evil that will continue as long as tech keeps getting better. Some are simple enough - a new weapon variant gets a new designation and a visual overhaul, some are fidelity-based - we can create objectively more complex objects. Some are a combination of that and design imperatives - Chief's armor being a notable one - it has changed in every single game, in some ways just to approach dated looking industrial designs that were exacerbated by early low tech. Sometimes that also means a Mjolnir variant upgrade.
Those changes are sometimes the easiest and sometimes the hardest to communicate or justify.
Story is tougher - there are spackle-y things that are necessary to patch together small canon issues (PoA orbital position in Halo Reach, for example) - and game-specific issues that were tongue in cheek, but need to be firmed up - Sgt. Johnson dying in Halo CE, for example.
It's an ongoing process, but certainly I think really old school fans of stuff like the early Nylund novels, and deep "never before exposed to the public but known about in Halo nerd circles) will genuinely embrace some of the stuff we have planned for the future.
Why is he talking about H5 while H2A is supposedly the main focus this year?
I can confirm he is more or less talking out of his ass, or by proxy talking out of his "source's." I am not confirming or denying anything specific, just confirming that he has no special insight or information.