Or moving Villanueva from TE to LT? Or Nix from DT to FB?
WRs get moved the DB all the time. It usually happens in college though. I bet Coates would have been a DB at most colleges, but he played at Auburn where the use a run heavy spread option. He was a good blocker and when Auburn did pass, he was often running free downfield and still had his share of drops.
i bet if he played on a passing team in college, he probably would have been switched to DB already.
the steelers need to go into the offseason looking for a deep threat outside WR. In terms of planning, Coates is to the WRs as Jarvis is to the OLBs. If he has a breakout, great, but you have to plan on replacing him.