You are right about this 100% percent, performance is not the only factor, especially in an established DB space such as a relational DB world. There is a lot of things to consider before moving/or picking the database.
But you can bet if such a car was announced, a whole bunch of people would be lined up to take it for a test drive to see if it really got the claimed mileage. If it met those claims, you can also bet that investors would line up to help iron out any kinks in the system that might keep customers from buying it.
Why is this not true for data engines as well?