Having worked in exactly the same domain , I can very well say that OTA is risky, moreover the data providers for the car is not really happy about OTA ( Sprint , AT& T provides connectivity for the projects I worked on.). They lease out a certain bandwidth to the connected cars which sends small bursts of data at a low contracted price. If the car manufacturers need OTA, they will have to pay a premium which will be slapped on the customer. There is also a technicality of downloading a huge image ( possibly 1 GB ) over a spotty network. ( a running car will switch cell networks , network types 3G , LTE , 1x , lost connections etc ).