i'm on an SE. i got this phone fairly late into its life cycle and it was a deliberate choice. my biggest regret is probably not getting a second one before they discontinued it because when my current SE fails i have no idea where to get a replacement.
I bought my wife the XS, not because it has a fancier display, but purely because it was the smallest model available - and it's still too big for her.
Instead of differentiating their phones based on features, they should simply differentiate them based on screen size. That would allow them to meet several price points without making their customers feel like they’re cheap.
Remember, the SE was released outside of the usual iPhone release cycle in March 2016, so I think intent for a longer cycle was clear.
Lots of people predicted between 2 and 3 years before the SE got an update, so if March 2019 passes without an announcement, then who knows what's next.
Also, I think there's a high probability they're trying to work out the kinks in an SE-sized phone that is all screen. I'd be surprised if they released the SE2 and it has a home button.