@AlexT:
In addition to the video output variants you have already mentioned i think "DisplayLink" should not be forgotten. I have such a monitor, it has to be connected to usb and it is supported by the kernel modules "udl" and "udlfb". Would be nice to see them activated in your kernel.
It can be used like any other graphics card with X. Indeed it's too slow for watching videos but nice for all the other things.