Good point. There are zillions of tokens for nearly everything we do in real life. Using an existent cryptocurrency like Bitcoin or Ethereum to pay for gas, seems like the ideal choice to make. However, I believe that making a token specifically for this, would allow mainstream companies to track their sales easily within the blockchain. They could also reward their customers with ease, than using ordinary cryptocurrencies we know and love today.

But who knows? In crypto land, anything's possible. Depending on the underlying blockchain network's level of scalability, companies will use them for mainstream payments. Bitcoin's Lightning Network seems like a great option for gas stations because of its instant TX speeds and very low fees. On the other hand, Ethereum's Raiden Network (similar to Lightning Network) proves to be a great solution for quick ERC-20 token transfers. Any mainstream company could decide to use existent solutions in order to drive adoption of blockchain technology within worldwide gas stations. The idea is there, but it's up to these entities to make it a reality. With the extreme popularity Blockchain and crypto have obtained over the years, you can expect to see something like this in the not-so-distant future.

Nonetheless, there might be other important things to focus besides using Blockchain technology for paying at gas stations. I mean, the idea is great but many people today are still comfortable using Fiat for gas stations worldwide. Experiencing a change in how payments are done, will prove to be quite troublesome for everyday people (especially old generations). Hence, this might take a little longer than expected before we'll be able to use our favorite crypto at a local gas station. Just my thoughts