It's a huge subset.
If it makes you feel better to describe it that way.. power to you. But I'd be generous to say it is even 40% of the applicable market. Add the fact that you can only get a subset of the market segment for various reasons, and it is, with no doubts, a limiting factor today.
The whole "rental car" fallback is so tired. People want to drive their own cars. They don't want to rent one. Yes, there are some exceptions, but it is small group. And saying the use case is one long trip per year is really reaching as well. That's an even smaller segment of the market.