I don't think GT8 will go full service model. Sony seem to have realised during the aborted The Last of Us Online development that letting their core, 10m+ selling studios - Naughty Dog, Guerrilla, Insomniac, Santa Monica, Sucker Punch - do what they do best is better for their brand even if the revenue ceiling is lower, and instead leaving the live service stuff to studios they've bought for that purpose like Bungie, Haven and Firewalk, or to studios they contract IP out to like Arrowhead.
Polyphony have been doing some form of "constant updates adding content but not seasonal live service/constant monetisation" since GT5 Prologue now, it's clearly how they want to work so unless they get mandated to change or their games stop selling then I don't think they will.