Who can we write to in order to complain about this?
I guess you could write BMW NA - though I don't think they will pay much attention to a request to upgrade/update a four year old car, in a discontinued model line.
One of the reasons BMW didn't add Android Auto until 2020/2021 and then in only some of the model lines. is that although Google launched Android Auto back in 2015, it has been slow to push the wireless version out to car manufacturers.
The other is, when BMW looked at adding phone mirroring, they surveyed their customer base, found the majority were iPhone users, so they started there.
2015 i3 Rex, Capparis White, Tera World, Technology & Driving Assistant, Parking Assistant, Harman Kardon Audio System, 19 inch Rial X10-i wheels, EVoInnovate EVSE