This franchise could go on seemingly indefinitely if it wished, which means the fact that the creative team has an end point in mind is probably a good thing, allow the franchise to go out on–theoretically–at least a somewhat high note rather than cashing those paychecks for the sake of cashing paychecks.
The interview happened before The Fate of the Furious absolutely dominated the box office around the world, although it should be noted that domestically the movie sagged just a wee bit during its opening weekend.
Regardless, just because Dom, Letty, Roman and the gang might be done after 10, there’s always the world of reboots out there that could make some cash.
Still, it’s safe to assume that money is not the motivation behind the endpoint.