The move to standard engines is inevitable, and not just for Halo.
It is an industry-wide trend rooted in economics and efficiency.
Maintaining a small army of developers working on an inhouse engine only pays off if you're a big publisher and you deploy it across multiple *big* franchises. EA and UBISOFT manage it. ID, TOO. Alternately, the engine needs to be uniquely specialized like BETHESDA's CREATION ENGINE, with its focus on physics and NPCs.
This isn't to say SLIPSTREAM has no redeeming value but it is a matter of record that the delays and cost overruns of HALO INFINITE were rooted in trying to modernize it. Likewise, the big gap in Bethesda RPG releases owe a lot to the challenges of maintaining and updating their engine. It's saving grace, for now, is that it enables a unique type of game that while it has a very specific audience, it is a big and committed audience that values the replayability and mods the engine enables. For all the FUD and badmouthing STARFIELD gets over its XBOX exclusivity, the game is very much a success both financially and creatively. At this point it is clear large numbers of people will still be playing (and paying) in that sandbox five, ten years from now until a sequel arrives.
For Halo, the biggest challenges are going to be moving FORGE output and multiplayer to the UE5.x runtime. Non-trivial. But the reward will be getting more regular releases, better aligned to the hardware of the day. Which isn't to say Halo will move to a COD-like annual release cadence but it might not be too much to expect biannual releases on four year cadences of two distinct product lines; say the MASTER CHIEF timeline on one side and ODST or HALO WARS on the other, both alongside the online multiplayer Forge-driven sandbox. Quite doable if the staff numbers devoted to slipstream are applied to game development.
Halo has been the XBOX's premiere IP for most of its existence.
It still can be.
But a revamp was overdue.
The gaming world is changing and the studios need to adapt to survive.
Finally, while no games have been announced, it doesn't take much to guess a HALO CE REMASTER is on the table for 2025/26, with a new Master Chief Release for 2028 following.
What is particularly interesting is the timing of Halo announcements in the past few weeks. A bigger reveal seems to be in the offing.