We should use Pereira as an alternate in the midfield three, and build an in-house succession plan for the future. Carrick is no spring chicken, and Bastian will likely leave at the end of his contract, so Andreas should get a lot of game-time as the latter's long term replacement as the prime mover of the team, especially when Carrick starts to fade. He has a lot of qualities that lend themselves to a midfield architect role, rather than a more attacking one further up the pitch (where the competition might prove to be even higher with the presence of Memphis, Mata, Di Maria, Januzaj + probable future additions).
He already has a great eye for the defense splitting pass, knows when to keep the ball and when to play the one touch football, knows how to dribble effectively from deeper areas, likes to get stuck in and doesn't shy away from tackles; the touch and precision while good is still a bit inconsistent, but will develop further over time with experience and proper training. In some ways he's like a younger, less refined version of someone like Deco who could go either way.
If we could train him under Schweinsteiger, bring him along at a slow pace considering his age, and teach him how to control the rhythm of the game (something Bastian learnt in greater detail under Van Gaal himself), then Pereira has all the talent to be a special central midfielder for the club, and will start coming into his own at age 22 by the time Bastian packs up his bags at United. Perhaps Louis could completely Schweinsteigrize him under the guidance of the prototype himself ?