As of now we don’t even know the year Halo infinite will be releasing as no year has been announced (probably due to 343 just finishing the engine). So what does this mean. Well story wise 343 have had time to get together and build a story long in advance of game devpopment as the game engine doesn’t impede on story scripts. Art wise, assets such as textures and models can be carried over from engine to engine and can be made out side of the engine they are currently using, so the textures and artstyle we saw is probably quite developed compared to everything else. Gameplay could see the most change, as only recently has there been an outcry (not unlike the one about artstyle) about the current gameplay direction. If 343 were to release next year this outcry would most likely do nothing as it’s too late to change key game mechanics that are already implemented, but it seems that Halo Infinite is far from finished. With this in mind we might see a mix between classic and modern halo as a response to this feedback. With that being said i might be wrong and Halo Infinite might release next year with modern mechanics but it isn’t out of the question.
We really do not now how far into development Halo: Infinite is right now. The fact that they “only” showed a in-engine tech demo/announcement trailer does indeed imply that it is still in a relatively early development stage, so any proper discussion regarding game mechanics will have to wait until we get some gameplay and hands-on experience. With that said, they did say that they will be following the MCC’s example of limited pre-flight testing, so we will probably get to play the game sooner than expected. Granted, said flight testing will come with a metric ton of NDA clauses but still it is something to get excited about.