OLED screen sizes beyond 77" would not be a hot topic IMO because the cost would be astronomical. A Z9D 100" is already $60k. A 100" OLED would be at least that much or higher. I would think they would focus more growing the OLED market than >77" screen sizes. How many people would be able to buy a $75k TV? Besides, since Sony doesn't make OLED displays, that wouldn't be on them, anyway.
Talking about OLED displays, sooner or later Sony will likely switch to displays from JOLED instead of LG Display. When that happens, THAT will be the biggest news to hit the OLED TV industry. 1) it will broaden the OLED display market, which is currently owned by LG. 2) It will introduce RGB OLED (LG uses WOLED), which will allow for much brighter displays. The delay on this would be related to when JOLED can create displays at 55" and 65" sizes. I suspect it won't happen in 2018 -- more likely 2019.
As long as Sony gets their OLED displays from LG, the only differences would be in the chipsets and external features (e.g.: HDMI 2.1), which, to me, is ho hum. Wake me when RGB OLED hits the market.