After Truvada goes generic competitors will still need a boosting agent like GILD's cobicstat to compete directly with the Quad (if approved). This provides another barrier to competition.
I thought that cobicistat is needed because of the elvitegravir component which needs to be taken twice a day if not boosted. If a competitor has an integrase inhibitor such as dolutegravir that can be dosed once-a-day without boosting, then they would not need cobicistat.