There isn't that much to write, Matchbox has enough to make X11 touchscreen friendly. Really it's just about all the hardware stuff which they've done before I'm sure.
Seeing as the screenshots are from Gnome, I'd be surprised if they used X11, considering Gnome's future is on Wayland. Not to mention the irony of shipping a "secure phone" with X11...
I still feel like being tied to X would be better than being tied to android. I use X11 on my laptop as do most people I know. Is it really that hard to just not run apps that you don't trust? There isn't that much out there that isn't built by a fairly popular open source project and is worth using.
With X11, an exploit in any GUI application can be turned into a privilege escalation vulnerability. On Wayland, to achieve the same, an exploit in a GUI application would need to exploit another application running with higher privileges to escalate.
Not running apps you don't trust is an overly simplistic security model, and completely ignores exploits.
