Is the PLUGABLE USB 2.0 HDMI/DVI/VGA ADAPTER FOR MULTIPLE MONITORS UP TO 1920×1080 compatible with the ASUS Chrmoebox yet? Seems there was talk about 8 months ago that Chome OS 49 would support it.
Yes, the UGA-165 is compatible with the ASUS Chromebox. Just one caveat is that you still can only run/have two monitors in total.
Update: Just tested the dev channel which is Chrome OS 51 and there you can use three monitors.