From the HDMI input:

#	11-13" screen of at least 1080p (1920x1080) resolution
I say be open to smaller sizes (10") and lower resolutions (720p)

#	usable outdoor (matte?)
sure but glossy works as long as its bright enough

#	dream: 3.5" headphone possible?
Of course; my AC100 us iPhone style that also accept headset on same plug

From the internal USB hub:

#	touchpad with mainline linux support
redundant with touchscreen.  I say omit

#	dream: uvc-compatible camera?
not difficult

#	mic? mic also available in the 3.5" connector?
see above

#	dream: SD card reader
not difficult

#	dream: schematic
I can do this.  Just lazy/busy