I've been playing around with the room parameters in the Cab block as well as a couple of Reverbs in an attempt to somehow emulate what the FullRes IR does. I've come close enough to see the benefit; it's one of those things you don't know is missing but when you hear it and play with it awhile, it's something that is hard to do without.
As far as whether or not to implement on the Mk1, it's a new feature that can be added without completely removing an existing feature (User IRs) or affecting the overall performance. I haven't heard an explanation of how reducing the User IR storage from 2048 to 1024 slots impacts their workflow or use case.
I understand the convenience of storing IRs on the unit, as well as needing them stored for use in existing presets, but why the need for more than 1024? How often do users actually access both User banks? Do people really even have 1024 IRs that they must have access to on the Axe III? If so, please explain how you use them or the scenarios you need them for. I'm legitimately curious, I love learning new things and different approaches to creating tones and using my gear.