The article still applies even though it was written mid '17 (the only difference being that larger screens are more available and affordable now). You're right on all the above and I think that the article is attempting to keep things simple. Sound wise your also right in the zone.

The 1.1x-1.3x is perfect for movies at 4k and covers the the non-4k upscale problems. Personally I'd be willing to sit at 6' from a 77" screen (0.93x) if 4k content was more available and my wife would let me. As far as eye strain I'd have to try it. Anyway, I had a hard enough time convincing my wife on getting a screen bigger then a 55". To her the 77" is huge. To me it's ok, an 85" would have been better and if I weren't afraid of people touching the screen a 100" UST would have been the best I could have placed there. I'll do better in the HT if I ever get to it.

The original point was that 8K in a theater is probably a waste of bandwidth. I believe everything you stated agrees with that point. Also I agree with CV's point ... when going VR, 8K will probably be a winner as you want to cover your peripheral vision to be fully immersed. I think VR screens would need to be specialized for that purpose ... i.e. extremely curved and that they will mostly be worn.