Publishers would just advertise their games as coming with a 2-year subscription, or whatever. People would have the same expectations as now: the game will be supported for a couple of years, and it will be supported much longer if there's an obvious way that is profitable to the developer.
No publisher would unilaterally want to start advertising games as subscriptions, but if everyone was forced to do it, nothing changes. Perhaps an extra layer of clicking through for the user, like when we mandated all websites must have annoying cookie popups.