Even though I have the 6GB version (EAN 4718017104913), most points remain valid for this 4GB version as well (see GSMArena for detailed specs of different versions):
+++ Lineage OS (that also means also unlockable and rootable)
+++ Dual SIM AND dedicated microSD slot
++ taller than Full HD (nice for reading)
++ big battery 5Ah
++ supports Galileo (at least with LineageOS)
++ many supported LTE bands (regarding Europe/Germany)
++ reasonably small size (no phablets anymore, please)
+ 3/4/6GB RAM (go for 6GB, it's worth it)
+ 32/64GB flash
+ no crappy back made of glass
I did a lot of research based on all devices available for Lineage OS (several hundreds actually!) and nothing was really fiiting perfectly- in the end there were very few phones left:
Galaxy A5 2017, Moto Z Play, Xperia Z5 Dual, Xperia Z3+ dual, BQ Aquaris M5 and BQ Aquaris X5+
... but then I stumbled over this:
Asus ZenFone Max Pro ZB602KL 6GB/64GB Dual Sim
aka ZB602KL, X00TD, EAN 4718017104913
It has all the features I want/need and better:
7 LTE bands (of which 5 are supported in Germany)
1080 x 2160 pixels (thus bigger than FHD)
fast 8xCPU (Geekbench SC 1336, MC 4687, really fast - zipping 500MB took only a few seconds)
...and last but not least: A HUGE battery with 5000mAh! The battery life is as promised - GeekBench scored 7432 which is better than most tablets (basically I expect it to charge every two or even 3 days, despite intensive usage), Screen On Time (SOT) can be expected around 12h.
Even though I wanted a much narrower phone originally, I am very glad with it - it has good grip and be handled with one hand.
Fun fact: It is much better than most phones but did cost only 220€. A charger, cable and even a simple case were included.
PS: An update for Android 9 aka Pie has been already released as beta, so it is up to date (still, personally I'd prefer LOS).