Naughty Dog have 300 people working for them, they could afford to put a team on the next Uncharted, while they develop a sequel to The Last of Us or make another new IP.
Guerrilla Games has around 270 people, the last statement I read from them stated that they had 150 people working on Horizon, while Cambridge have said that 70 people are making RIGS.
Hell From Software has fewer staff than Guerrilla and they developed Bloodborne alongside Dark Souls 3.
London could potentially spare the resources if they're not making some big AAA projects internally, I'm pretty sure they had over 300 people working there, though they haven't announced anything big since they went silent on Eight Days and The Getaway.
Santa Monica are known to be working on a new God of War, plus they help out on smaller projects, may potentially have other new AAA projects in the works, so I don't know if they could spare staff for Uncharted.
TBH I think the best bet for Sony would be to source new staff for a new AAA studio to work on classic franchises like Uncharted, though it would require a lot of incubation time and some very skilled, experienced people, under guidance by key ND people to make it work.
Maybe Amy Hennig could return to Sony after she's finished working on the Visceral Star Wars project and then helm a studio dedicated to Uncharted, but it would depend on what happened between her, Sony and Naughty Dog.
