It's going to be a real letdown if it's iPhone 8 size; we're so lacking in high-end (or even midrange) phones in a small form factor now. There's nothing on Android either - even Sony's Xperia Compact line is now much bigger than an SE.
You could fit a 5" screen on the SE form factor if it was edge-to-edge like the iPhone X, or you could keep the old SE 4" screen, make that edge-to-edge, and make the phone itself even smaller.
Illustrated: https://i.imgur.com/OKZiWrN.png