The other issue is that studios generally feel a need to put a carrot on the other side of the gate. At the moment, I'm tracking Warframe and the current update has (essentially) pay gated zones with a reagent drop that drives both additional character progression and player housing. Neither is necessary to complete any of the other content in the game–the game has a mechanics problem where weapon damage scaling is excessive, the relative ease of content clearing is one–and the playerbase is whining about P2W.
My inclination would be something like:
* Subscription based
* Sub payment produces in-game tradeable item, time added on use
* Subscription use suspends X days after not logging in
* Payment auto-renewal only triggers when 2 days left
* You start off with X weeks of playtime
I haven't actually seen it done, probably because it's not a reliable recurring revenue stream like traditional subscriptions and isn't that strong of an impulse buy. I have seen somewhat similar ideas in a game with limited moves per day but from memory (been a while, blanking on the name) they also used the time item as a catalyst for weapon upgrades which for me veered too far into P2W so I dropped.