I already did a build for 16.04, without any changes, but it has issues with apparmor.
It's only working with 'template: "unconfined"', which is the reason I did not publish it to the openstore yet.

Yes, do a fast release.
Currently (before last OTA) there are so much fixes, that the stable users have to wait for one or two months.
I think it's better to get fixes to stable channel quick.

just use the email-client dekko2 (https://open-store.io/app/dekko2.dekkan)?

Ah, I was a little bit wrong: All SIM-pin entry screens are like this (on 16.04-devel FP2):

And PIN / password to unlock display is like this:

@dobey , @Flohack :

But when returning from flightmode, to unlock the Simcards (on FP2), the old screen design is still in use.

@matteo : No I did not cut that output. I did not connect my device, because I thought its not necessary and it would proceed building anyway.
I thought the error is, that it does not find the requested image container at https://sdk-images.ubports.com.

Just want to add my findings in trying to use crossbuilder:
Ubuntu 17.04 (32bit)

setup-lxd without zfs went well.
When trying to build with "crossbuilder --ubuntu=16.04" it stops with this error:
https://paste.ubuntu.com/p/YzNbHgGPpJ/

Yeah, that doesn't look very promising.

Meanwhile they are working on wayland support (https://support.displaylink.com/forums/287786-displaylink-feature-suggestions/suggestions/16639654-linux-wayland-support).

Mh.
But its working without problems on the FP2 with android.
And Linux is officially supported by startech.com (https://www.startech.com/AV/USB-Video-Adapters/usb-3-to-hdmi-adapter~USB32HDPRO)

So I decided to buy a DisplayLink adapter by myself and.... meh:

phablet@ubuntu-phablet:~$ chmod +x displaylink-driver.run 
phablet@ubuntu-phablet:~$ sudo ./displaylink-driver.run 
Verifying archive integrity... All good.
Uncompressing DisplayLink Linux Driver 1.3.54  100%  
DisplayLink Linux Software 1.3.54 install script called: install
Distribution discovered: Ubuntu 16.04.5 LTS
Unsatisfied dependencies. Missing component: Kernel version 3.4.0-g8826794 is too old. At least 3.14 is required.
This is a fatal error, cannot install DisplayLink Linux Software.
phablet@ubuntu-phablet:~$ 

Is there a chance that the kernel will be updated with a newer android-version vor the FP2?