New game engine, putting aside concerns of Epic exclusives and such, seems fine,
but changing the name, it's not to signify the game studio will focus on halo, 343's name is based on the franchise;
"New name, new philosophy", it's trying to distract from the past trying to say "under new management", but in recent times companies have used this as smoke and mirrors, hiding that nothing has changed.
I'll believe new philosophy when a game comes out that isn't trying to be destiny or cod and doesn't have 50% of the game missing at launch because of mangled management that was fine shipping an incomplete game and never finishing it.
All that time and effort into developing Slipspace right into the toilet, and now Halo will have the same buffer stutters and other known issues that modern Unreal games suffer from. I don't like how samey the industry is becoming. Why not improve the purpose-built engine? Saving money, I guess... At least I've still got Halo 4...
While your point is valid I think it may actually be a good thing in the long run. As MS only allows contractors to stay 18 months this may help get people on the same page faster instead of learning a proprietary engine. Instead of teaching people they can just look for people with UE/5 experiance and get a game(s) out faster.