However, if we take into consideration the fact that Satoshi was thinking of the blockchain growing by 100 GB every day, then it's probably plausible to assume he'd envision cheap on-chain transactions. As I have mentioned before, Satoshi is not the ideal figure to be regarded as the unquestionable authority or ultimate arbiter of truth for Bitcoin.
I assumed that 100 GB per day was meant to be further in the future. But just imagine that: that's about 500 million Bitcoin transactions per day, which would mean mass adoption has been reached.
some merchants will hesitate to accept card payments for a soda drink
It's funny you mention that: here, it's the opposite. More and more merchants including government institutions refuse cash, and only accept card payments. We're a debit card country though, so fees are a lot less than with creditcards.