Fergie played Powell about 5 times. Don't see how you can say what the plan was for him. Most of the time for the u21 side he played behind the striker or as the front man. Same with Wigan.
Nick only played as a striker for the u21s because Gohan, Macheda, etc... went out on loan. United had no striker so they put him up there often switching with Januzaj. Then he became injured and missed the rest of the season, which resulted in Lingard/Januzaj as the main striker for the rest of the season.
His time was almost equally split between midfield, in the hole, or as a striker. I'm going to guess that he spent a little more time in midfield for the reserves. He played in midfield this season for the reserves too, although that was a really short stint before going out on loan to Wigan.