I have been wondering for a long time about this, and even though there have been no announcements yet, I am thinking the next Athearn N Scale steam locomotive is probably going to be the FEF series. My thinking is based on their previous releases. First the Big Boy came out in HO, then after some time, they released it in N. The same goes for the Challenger. Given the fact that the only N versions right now are brass, and the widely known popularity of 844, a high quality plastic FEF could be a popular item.
Josh