So if we are talking about 10+ years long term outlook: income will only be as high if Tesla's solution is going to become a de-facto monopoly, and they can price their taxi services to around the pricing of human driven taxi services.
Otherwise if there's competition then robotaxis will set the price of taxi services to below that of human taxi services, human taxi services will gradually die out and robotaxi services will conduct a usual race to the bottom, prices somewhere around the price of expected capital returns.
I.e. the very long run lower price target for a $50k capital investment will be ~5% of the capital, $2.5k/year, or $25k over 10 years.
But in the initial phase they will track taxi services pricing, and will generate 10x higher returns - especially if Tesla becomes the dominant leader in the segment, which they have every chance to achieve.
If safe and convenient robo-taxi is achieved, I guess the adoption rate will be a reverse function of per mile fee. If the fee is $1 per mile, the demand probably can reach 2 trillion miles per year. If the fee is $0.4 per mile, demand could reach 6 trillion miles per year.
Tesla said their own cost will be less than $0.18 per mile (tire, electricity, depreciation, etc.) My calculation arrived at the same number. If only Tesla has large scale robo-taxi services, they can charge $1.2~1.5 for a long time.
If 4~5 companies all achieved FSD, in theory nobody will make much money on robo-taxi, in reality their own per mile cost will make a big difference.
A $100k robo-car that can last 300k miles will have an all-in per mile cost $0.46, the company has to charge above that number to break even. Meanwhile the company with $0.18 cost can happily charge 0.4 and take the whole market - $2.4T revenue and $1.32T gross profit.
The third scenario: other companies started FSD ride sharing, but Tesla Network somehow get delayed for a long time.
The true winner need to get both right: a large scale FSD network; per mile cost is very low. It may be a good idea for Tesla to quickly start a pilot taxi program in one city, initially supply safety drivers in the cars. They probably can gain a lot of insight by doing this, also can help to sell cars in that city.
Ultimately, the most important thing is to achieve safe low cost FSD. Tesla is missing the last piece, which is the hardest piece.