Coins with low value need wide adoption before they stop being shit coins... It makes no sense to make micropayments with coin as valuable as Bitcoin, but it doesn't make sense either to use some "cheaper" coin that can't be easily converted to FIAT due to low volume on exchange(s) it is listed on.
There is also a lot of coins listed on exchanges with bad reputation, either because the fees are too high, the customer service is subpar or because the markets are too much manipulated, so getting decent exchange rate is unlikely.
A lot of coins that would be good for micropayments don't have mobile wallets as companies like Google and Apple charge high fees for access to their app stores or developer tools.
BCH I think is used on this read.cash platform for payment, its doing well, for me its a shit coin though, but as of now I think it is functional with good volume to be accepted as payment.
Lots of options should be there actually, but this Tesla guy is hyping up Bitcoin with this move, his intention is not anabling crypto payments for those cars, its just create hype on bitcoin, that's all. Why he can accept payments in ADA, XML, any stable coin, ETH (ouch the fees), DCR (decreed), Atom why even HIVE right?
BTC is ok he can accept payments in BTC, its cool, no problem, but he is doing it as advertisement for Bitcoin that's all... he can advertise Doge coin also, accept it for payments why not?
Dogecoin would be pretty good for smaller payments... But there is a big risk in using Dogecoin due to high volatility... Basically accepting payments in Dogecoin when its value is at or close to all-time-high, the seller has very big chance losing when the value starts going down closer to the equilibrium.