I've got the Sony 84" 4K. I selected it after seeing the LG (84") and Samsung (85"). Although both of these other models (LG/Samsung) also have excellent images, I believe the Sony did a better job of processing. I also did not see anything in the Samsung that would cause me to spend the additional $15K for that panel, backlit or not. I have not experienced any of the issues that can sometimes be seen with edge lit displays.
Coincidental to your question, today I finally received confirmation from someone I trust at Sony that we (84" 4K owner's) will be upgraded at the appropriate time, not only for use of the X1 (we already have the Dell 4K Player), but to whatever HDMI spec is released to support 4K (the 2.0 designation has not been confirmed). That said, at this point it's a trust issue for those buying with the understanding an upgrade will be available. Personally, I didn't buy it for the 4K, I bought for it's size and the image it currently produces, so although I'd like the upgrade support, if it doesn't happen I'm still fine with the purchase.