If cars could assemble into close convoy trains on multi-lane highways / motorways / autoroutes / whatever, then it would probably also solve electric car range for many people - you only care about range on relatively long distance journeys, and you're likely to be doing those on major multi-lane carriageways. If you could split the air resistance between a bunch of other vehicles then you'd add considerably to the range. I similarly don't understand why we're not trying to solve that instead. As you say, it seems easy compared to full autonomous driving.