I really do doubt OLED will ever make it to 40+ inch display's. OLED still have a lower lifespan comparatively, not to mention high power requirement. And even if they do, I would say it would have the same fate as plasma TV's.
At this point QD-LED seems like the only alternative present. As long as they get over manufacturing issues (which will eventually be solved IMO), I guess we will really be seeing this displays within a couple of years.
Though I guess one advantage OLED have is that they are flexible, so yes, I guess we won't be saying goodbye to them for a long time either.