Oh yeah that reminds me, I just happened to read last week that the YouTube app in my Sony smart TV (circa 2012) is not going to work anymore. I imagine the same for many other brands as well.
http://esupport.sony.com/US/p/news-item.pl?news_id=487
I also have a 2012 Sony HDTV model (KDL-40EX640) which lost the YouTube app, but thankfully for me, I have a 2012 Sony blu-ray player (BDP-S590) connected to it which got a new YouTube app a couple of months ago to replace the old YouTube app. Three years ago, I almost bought the cheaper BDP-S390 model (which also lost the YouTube app) but, decided to spend a little more in case I wanted to take advantage of the 3D feature of the BDP-S590. I never bought a 3D HDTV, but it looks like it was still a good decision to get that model, otherwise I would be looking for a new smart blu-ray player in the next week or two. You never know.