Popping back in this thread just on this...
That speculation on its own doesn't make sense next to the CMA's final report IMO - Acti games on gamepass was the one thing the CMA recognised as constituting a consumer benefit of the deal. Just keeping games off gamepass in the UK not only quashes that but does nothing to address the concerns they did outline in the final report (i.e. around how licensing of 'important supply' would operate post acquisition, and Microsoft's control over same). The only way the CMA would be satisfied with an approach like that is if they're no longer looking for a solution to their concerns as actually outlined, but instead just 'anything' that looks like a compromise on Microsoft's part (which they might - but it would look insanely incoherent as a solution for anyone paying attention to what the final report actually said).
What could make sense IMO is Microsoft divesting itself of UK cloud licensing rights for Acti games, into a UK company, and that when cloud vendors want to license Acti games for the UK market, they go to this independent company instead of MS. So 'Acti UK Cloud PLC'. That might have the side effect of meaning that Acti games won't automatically go onto gamepass (or perhaps more exactly, xcloud) in the UK, but that would be just a consequence of that set up rather than expressly what the set up was designed to do (as per a 'GamePass UK PLC'). In that kind of set up, to offer Acti games on xcloud to UK customers, MS would have to go to this independent company like any other vendor and negotiate/compete for the content, and that would satisfy the concerns the CMA outlined. And they might say that Acti UK licensing will continue to operate independently in the meantime until this structure is set up, to let the deal close immediately while the CMA process winds on.
In that kind of set up, the bottom line impact for UK Xbox customers is that content wouldn't automatically be available on xcloud streaming and MS would have to do extra stuff to make that happen. A more limited impact than content not being on gamepass at all.
(Am putting aside for a moment that this kind of setup would arguably be something the CMA would have issues with previously, and might carry behavioural components, single economic entity components etc. - but this might be the compromise the CMA is willing to make now)