There's no problem for tesla by adding doge as one of payment sistem. Nothing wrong with it. This is also adding the real usage for doge coin in real life but basically, any crypto can be used to buy tesla as long as they do have the value. It's not always focusing on doge coin.

Some things that pushes tesla to accept doge coin is


-Big liquidity
-Widely accepted by many exchangesites.

I think that the problem related to the volatility of coin can be solved easily through doing instant transaction. Doge has good scalability and this can also be used as sense eason to accept doge coin as a payment too.
doge coin can also be accepted even in the various store as well. The key is about how fast the store cna validate and exchange the doge coin into the FIAT asap.

This has been planned by elon since last year but it's executed this time.