according to what i know
the reason nethunter is only available for nexus & oneplus devices are because they are cheap & globally available
but now we have many more companies which sell smart phones globally & their phones are much cheaper than a nexus or oneplus phone
for example Xiaomi redmi note 3
it also have OTG so we can connect external adapter for wireless pentesting & it have a huge 4050 mah battery
what do u think guys ?