I think that the only differences will be superficial as in trim levels, finishes etc between the Lincoln and Ford Expy. When I went shopping in last November, I glanced at the Navigators sitting in a row but didn't like the "look" of it so I never walked over to see the inside of the new ones on the lot.
I used to think there was a difference in the suspension package but according to the PDF manuals I have for the earlier years, I was wrong.
I've seen the pics of the '18 Expy and it's pretty slick looking but I'm VERY happy with my '17 ......and this is my third Expedition. The nicer suspension package found on the Platinum did ride better than my Limited but I made that decision when I bought this one and don't regret it.
To each his or her own but I could not stand having LED's for the fog lights but Halogens for the headlights. They didn't match and looked dumb to me so I swapped out the bulbs and installed LED's for the headlights and the grand total cost was 26 bucks and I LOVE how it looks now! That's the only thing in 5,500 miles that I've found that I didn't like, and it was changeable!
Good luck DL with whatever you choose!
jeff