Must be a better word than ‘niche’ there. Tesla sell cars, the best car available for $40k. Cars are not niche.
Perhaps ‘in early stages of scaling’.
You have a large subset of people who are not yet comfortable with the reliability, the lifestyle modifications, or the tech. Lots of stigma to shake off like battery dying after a year or car stop working if there's a bug in the computer for mass adoption. So by definition Teslas are still niche. If Tesla made 10 million cars this year, they wouldn't get 10 million orders.