It's hard to say who he's "replacing." Austin was in on 2 offensive snaps in the Packers game. In both plays, we were only in 2-WR sets, which normally calls for TO and Crayton. This wasn't the only time that Crayton was replaced in a 2-WR formation. Hurd replaced him on 2-3 plays. This was likely just a precautionary measure given that Crayton had injured his ankle just two weeks before.
However, on all 3-WR sets, the typical lineup of TO, Crayton, and Hurd was used. I guess you could say that Austin jumped Hurd on occasion in those 2-WR formations, as a replacement for Crayton.
But the results so far speak for themselves. Austin was in the game twice on offense, and both times he got open and was thrown to.