Will X11 window forwarding over SSH still be possible in Ubuntu 15.10? Is there "cross compatibility" in Mir, or are there additional steps that need to be taken to allow such support?
I just run the current daily-live image in VirtualBox, and it loaded X. I proceeded to install it, and the installed version also ran X:
As you can see, X11 forwarding from and to the virtual machine worked fine.
Either the integration is flawless, or Ubuntu 15.10 still uses X by default. And since the final freeze happened some weeks ago, I think we'll have to wait one more release for Mir to be default.