How?
Pay an absurd amount of money for GamePass parity on ps plus?
How much would that cost?
It’s not worth it at this point. Sony isn’t going to spend marketing money on a Microsoft ip
The negotiations between Sony & ABK would have been done on the grounds of ABK operating as an independent corporation, not as a subsidiary under Microsoft. That's how they would have been legally required to operate prior to the close of the deal. And, at least back a few months earlier into the year, I'd say after the CMA's block, Sony had the most leveraging power.
They could have easily stipulated Day 1 exclusion clauses for Game Pass since ABK themselves seem generally apprehensive towards doing anything Day 1 for any subscription service. It would not have costed Sony that much, either. And, that's in addition to still having marketing rights, preferred early beta access, and various DLC & MTX perks. Anything Microsoft would have wanted would have been ignored, because they did not own ABK yet, and ABK is legally required to operate in the best interests of an independent entity until the actual acquisition is completed (and that's if it's even completed; back in March it seemed very unlikely that would have been the case).
Now maybe Sony will quit with 1st and 3rd party exclusivity so gamers can "look forward to a future where players globally have more choice to play their favorite games."
Nothing stops people from buying multiple platforms to access the games they want. Let's just stop this fake "pro-consumer" BS; MS have 1P & PLENTY of 3P exclusives too, as does Nintendo.
"Gamers" have no issue buying multiple devices to play their games. It's the weird single-platform types who either can't afford (not the fault of console makers BTW), don't want to buy multiple systems, or are shills for a very specific company, that have adopted this "exclusives are bad" mentality.