a) As far as I know the score visualization in PB is done with OpenGL. Android supports only OpenGL ES, so this part has to be rewritten.
b) the connection between piano and android is painful since there is no smartphone which has a serial port. So you have to use a special "MIDI to USB(-Host)" or "MIDI to Bluetooth" converter.
I have an ipad size ( 10" ) Android tablet with OTG - USB connector.
I try to connect my usb midi connector which is working well with my desktop pc.
If its working - why not?- standard usb device and linux- the only question will be the cross compile and rewrite necessary functions.