A hypothetical – since flights are relatively expensive, people usually just go for the cheapest option, so airlines race to the bottom and lose profits. With autonomous vehicles the cost of a ride will be very inexpensive–a few dollars probably–so consumers may focus less on cost in favor of brand loyalty, cool cars, etc, leaving room for providers upsell certain services and profit (turning a $4 ride into a $5 isn't a bad profit margin)
I’m sure they will try to hide that by offering subscriptions, loyalty cards, better chairs, larger cars, larger monitors, Netflix, faster rides, etc, but the competition will go wherever the demand is and offer that $5 ride for $4.50.
I’m not sure how well they will be able to diversify their product while keeping the economies of scale. If 10% of your customers is willing to pay for more leg space, can you get by with 10% of your fleet being larger cars, or does that affect the waiting times of that 10% too much, and do you need to make most of your cars larger?
Also, if you pay $1 extra per trip on your commute, that’s a nice smartphone each year.
I didn’t say that I would, nor that it would be “however small the difference”; I claim some people would. I also think that, if Uber and Lyft manage to capture the lower-income market, many of their customers will.
Also one man’s “reduced comfort” is another man’s “less luxury”. People make those choices all the times, e.g. when buying cars, train tickets, housing, or food.