I do not think most of the work here is engine-side, but client-side, and from what I've seen client-side in unvanquished is in need of a lot of love, so this is likely to be a quite hard work.
The screenshot in the link you said actually show the kind of HUD/GUI changes that would be needed. And my guess is, it would be pretty hard to play with that mock-up HUD still: it feels very cluttered, and shows important information in a place that is likely to be covered by the hands: health, number of ammo. Unvanquished would suffer the same problems.
A HUD like what red-eclipse have would be better while still not good: at least there, ammo information is shown on the middle of the screen, near crosshair. It would still not be good enough as the "health and stamina" and "weapons" info areas are still on bottom corners of the screen.
Maybe the HUD should be revamped before trying to port game to android? And by porting I mean a port that includes supporting other kinds of control devices, not just using those mini-computers as a desktop by plugging in there a keyboard and a mouse.
I guess it would require moving the infos that are traditionally bottom side on upper side, but then where to put the map? Lower-middle, maybe? This would certainly feel weird for PC gamers, as we're trained since decades to the kind of HUD unv currently have.