The number of WR that have had 1200 yfs has been on the rise the last few years. Went from 6 to 10 to 12 to 14 over the past 3 seasons. I would be inclined to vote no, but it may not be such a crazy thing to ask or consider.
No, it's not when you consider his rushing numbers. If he gets 300 yards rushing he'd only need 900 receiving to reach 1200.
Given the fact that only twice in NFL history* has a WR rushed for even 200 yards (Percy Harvin 2011, Bo Roberson 1962**), I would say expecting Tavon Austin to hit 300 would, in fact, be "such a crazy thing to ask or consider". 150-200 rushing yards seems reasonably achievable, but 300 rushing yards would be a historically impressive accomplishment.
* this could be three times, depending on how you deal with Josh Cribbs in 2009. He was listed as a WR, but much/most of his running came as a wildcat QB, and his rushing yards outnumbered his receiving yards by a factor of nearly 3 to 1.
** Roberson was in the middle of a position switch, playing almost exclusively as a runner in 1961 and almost exclusively as a receiver in 1963. Such position switches were quite common at the time, and several other successful WRs have eclipsed 200 rushing yards earlier in their career when they were still RBs. Eric Metcalf would be the most recent such example- he frequently topped 300 rushing yards as an RB in Cleveland, but only had 163 more rushing yards remaining in his career after Atlanta shifted him to WR.
Edit: Here's the complete list of "WRs" with 200+ rushing yards, as produced by the HDD. It's important to note that, for the purposes of the HDD, any player who was listed as a WR at any point during his career will be considered a WR for his entire career. Brad Smith and Josh Cribbs hit the mark as wildcat QBs, Metcalf, Taylor, Jackson, Mitchell, and Morris hit the mark as RBs before later being moved to WR, and Marlin Briscoe hit the mark as a starting QB before getting moved to WR. Briscoe is an interesting story- injuries forced him into the lineup for the Broncos as the first black quarterback of the modern era, but despite handily outperforming the other QBs on the roster, Denver cut him after the season and no other team was willing to sign him unless he switched positions.