SimGuruLyndsay confirms The Sims 4 has no planned End-Date.

I've suspected this for a while, based on the structure of the game. It's designed to last as long as possible, not to be phased out on schedule. And there's no value to EA to start all over again when all indications are that packs still sell well. All signs show that the game is profitable this far in; statements out of the investors meetings seems to suggest it's gaining players, not losing them. They're trying to get people to understand that it's not business-as-it-used-to-be for Sims.