I agree, can’t see why it will be any different.Why will it be any different to enforcing any other Standard plus/premium of First class? It's having branding added that's why it's not in use yet so nobody knows what that will look like.
I think the plan is the MK4’s will be every other hour with a 5 car in a 3+2 config with standard premium on the hours between the MK4’s.Ideally it needs to be on every Manchester-Cardiff/Swansea that isnt a MK4 if they want people to get used to this upgrade service.
As there will 13 3 cars with standard premium, they’re guaranteed to be on other routes so not sure how they will diagram them.