Was half joking about Button. He actually said STR (pre Honda) offered him a role before he retired and he turned it down.
However, he also said he didn't want to race in F1 if he wasn't winning. Chances are much higher he'd win in a RBR than the McLaren Honda he was in. They could use his experience to help with the setup too as they develop the new partnership.
Realistically, I'm expecting Gasly to get the seat, but it's fun to think about different pairings.