The experimental port of Arma 3 [Steam] for Linux has been updated today and we now have the much more up to date Arma 3 1.64.
This should also allow Linux players to play the Apex expansion/DLC, as the last time the port was updated was before the Apex expansion was released.
Sadly, it seems my texture issue is still around. Most of the time I can't select higher than "Standard" for textures. It seems this is an issue with the game being 32bit, although a 64bit version is being worked on for Windows. They haven't confirmed if 64bit support will come to the Linux port, as noted in the FAQ.
It's a truly massive update and it won't be possible to list all the changes here. You can find out more about the Arma 3 1.64 update here.