Digital signage solutions for Linux exist and work on the Pi. There even specific
ones advertised on the forum. Android is NOT plug'n'play with USB are hardware AFAIK ,
this has nothing to do with the Pi.
Android is held off either by the fact that
1) the community is unable (in a real technical sense) to provide a driver (i.e. no specs) or
2) the community believes 1) to be correct and doesn't like RE or
3) the community has not the required experience (not to be confused with 1. ) to enable HW accel. or
4) lazyness on my part , beacuse i'm not going to do it (especially when i have to do it a "nonstandard" way )
ghans