The report comes from Ian Rapoport of NFL.com who is saying sources are telling him that it's Mallett's turn to show what he can do. It will be an audition for 2016.
It's the best chance for the Ravens to really see what they have moving forward. With the team out of the playoff hunt, Mallett doesn't have to have the pressure of winning games on his shoulders and can just focus on going through his progressions and making the best case for himself. It will also help that the Pittsbugh Steelers have a rather suspect defense, giving up the 31st most passing yards and the 11th most points in the league currently.
Veteran Matt Schaub having shown what he can do for two games, mostly throwing interceptions that were returned for touchdowns. It seems very unlikely that the Ravens would bring him back next season as it is clear his arm strength is diminished to the point of being a game manager style quarterback even if he wishes to return next season.
Backup quarterback Jimmy Clausen has looked decent in his two starts as well, something that most fans and analysts didn't expect to happen. While both of those games ended in losses for the Ravens, it was important to see that he could make throws at every point on the field and did well with a pass rush coming in fast against him. Clausen isn't under contract for 2016, but would likely be available if the Ravens wanted a quarterback competition for the backup job under Joe Flacco.
Sadly, this is all necessary because of the injury to franchise quarterback Joe Flacco. Flacco tore his ACL and MCL against the St. Louis Rams, but was able to finish the game on his injured knee only for the report to come out as head coach John Harbaugh stood at the podium after the game. It is expected that Flacco will be able to return during training camp in 2016 and won't have to miss any practice or game time.