Yes, we'll find out soon.
I'd say it's not related to Local Hero Musical as far as there are no horns on it.
I'd say it's not related to the Teenage Cancer Trust/Buddy Holly Foundation as far as I think it's not worth the cost of bringing the American contingent to just one or two songs for the record, when McIntosh, Cliffe, Bronze etc are at a short travel by train or underground.
My guess is:
a) Extra stuff for the new record, that would mean delays, as Guy said it was mixed and mastered already so they would have to mix and master again.
b) Guy's statement could also mean the new MK record is already finished and what they are doing is work on next. That would explain the presence of the horns section. And why Guy doesn't says a thing and John and Richard deleted the pictures. As far as the previous record is not even announced maybe is too soon to announce a new one.
c) It is another different thing, a film score or whatever other project that involves recording sessions and the budget is worth bringing the Americans to London. I'm not an expert on this but I guess that their flights, hotel, expenses are also paid in the salary they get from the sessions, otherwise they won't move from the US, as they have plenty of work there already.