As an OLED Ipad Pro user, the blacks are indeed blacker, but I can't say I really *prefer* it over other screen tech. The lower battery life is the only feature that interests me about OLED (and battery life on my Ipad pro is abysmal and has been from day 1).
Re: the cellular option, I don't see why that's not an option. I still have (though rarely ever use) my old Ipad Air Cellular. If it can have a SIM and mobile data, I don't see why a portable notebook can't!
But practically speaking, I'm almost always in a place with wifi, and when I'm not, cant you just connect to your phone and piggyback off it's data? Apple makes it quite easy to do that. And it avoids a separate monthly line item charge for "notebook internet service charge."
I'm a MBA fan for life. Sorry but the 15" format is just perfect for me. Anything less is too difficult for my 40 yr old eyes to comfortably read, and anything more is too bulky. Of course, Steve Jobs was instrumental in the 15" MBP Retina (the famous "greatest laptop ever", which got everything right, and had ALL the ports (USB-A, HDMI, SD, etc.). but it's been a long time since we had a 15" "pro" option. The 15" MBA does everything I could want and nothing from this rumor makes me envious of the pro line.