If the iPhone 8 Plus , dropped to the iPhone 7 Plus price this year, as they will do traditionally, it will be prices at $669.
Which is inline with the projected price of iPhone 6.1" LCD.
So instead of getting a cheaper iPhone 8 Plus this year, your get the iPhone 6.1. For the same price you get:
5.5" 400PPI LCD vs 6.1" 326PPI MLCD. ( MLCD+ from LG )
A11 vs A12 -
Same 3GB Memory
Same 2x2 Antenna ( I don't know why some people are complaining, no other manufacture has has mass produced 4x4 antenna yet, they are only on a few flagship Android phones. )
Qualcomm / Intel modem Vs Newer Fully Intel Fabbed 14nm Modem ( Which I have high hopes for )
Touch ID vs Face ID 1.0 ( I seriously hope they give us FaceID 2.0 instead, 1.0 experience wasn't good enough for me )
Dual Camera Vs Single Camera ( I would love to see comparison on that )
Single Sim Vs Dual Sim.
Is that a good trade off? I don't know, we will have to see the Phone's display quality to judge. It is very hard for anyone to say feel internal component changes, like SoC and Modem. But everyone will notice the Display Difference. But from the Spec on paper., I think the $669 this year is a pretty good deal.
But if iPhone Xs Plus will be same price as last year's iPhone X at $999, I think I will defiantly go for the 6.5" screen instead.