I recently read a post somewhere (I hope it wasn't this thread
) where the guy actually removed his rear brake assembly because it weighed too much and was causing him to have accidents.
Using the engine to brake is fine and downshifting is optional. It wont hurt the transmission as long as you use the clutch.
But regarding corners. Its just fine to brake and downshift before the corner, but inside the corner, its easy to cause the bike to lowside if the rear wheel is improperly braked. This is especially true of engine braking where a miscalculation of RPM and gear combination could cause the rear wheel to skid and initiate a lowside.
But outside of corners, I engine brake all the time such as when I am coming up to a red light or stop sign - or when I come up behind a slug on a two lane road. In those cases, I don't apply the real brakes until I am closer to the stopping point. It would be nice to have some way to signal people and tailgaters behind me that I am slowing down.
Something like that could mean the difference between eating pizza by the road and BEING road pizza.