I love the concept of Armor Cores and am totally fine with them being limited to the components of each core (For example, you can only wear Yoroi variants on the Yoroi core, not the Mark VII) I’m fine with it because I have a decent understanding of character design as well as that the attachments and whatnot were made to fit with the core they were designed for. There’s little room for exception for this, and it’s why we see things like the MARK V helmet for that core and the MARK V ‘ZETA’ for the Mark VII core. They compliment their specific cores and can look wrong on the wrong core. Imagine how ugly a Mark VII core would look with Yoroi stuff on it, for example.
We know for sure about the Mark VII and the Mark V cores, along with Yoroi.
Here are some cores I think would be great in the near future:
MARK VI (Halo 2/3)
Take all the customization from Halo 3 and give it the Infinite treatment.
ODST
This seems obvious. Plenty of variants and options… and who doesn’t love ODST armors?
ONI
This theme could be pretty rad. New armors inspired by the Hunter set of Halo 5.