I wouldn't be surprised if, at some point in the near future, Apartment 1 is used by the Cambridge's, its been stated they want to stay there for years to come (code IMO until William is King) so more room will be required.
Either way, I don't think the Gloucester's were forced out at all, when W&K married it was said the Gloucester's offered to move out, and again when the Sussex's married. It may simply of been a case of waiting for somewhere else suitable at KP being available for the Glocuester's to move into. The Queen stated she wouldn't force Prince & Princess Michael out as she had promised them an apartment for life, when keeping them in it for free became too much of a problem HM paid rent personally on it for 7 years before the Michael's took it over themselves. Bear in mind this was for cousins who don't officially carry out royal duties so I can't see HM suddenly changing tack and demanding the Glocuester's, who have represented her all over the UK and world, downsize.
IMO this is the Gloucester's having no children at home, perhaps reducing their activities a little and deciding they don't need as much space as the massive apartment they inherited use of from his mother.