I wonder if one of the reasons why development took so long is because instead doing seperate halo releases in the future, every few years another section of zeta halo will be unlocked and the 6yrs of dev time has gone into building the framework to make this possible.
It could mean new halo campaign content could be released in shorter intervals.
Also maybe slipspace and infinite was designed to take full advantage of SeriesX/S, but because of the initial section of the zeta halo having to run on Xbox one there was not enough time and the lagacy of xbox one made current gen engine implementations impossible.
Hopefully the next section of zeta halo is xbox series/pc/cloud exclusive.
Also I would not be surprised if the next section of zeta halo was not broken up and completly open because of the SSD in current gen.