https://teslafi.com/firmware shows Previously Installed Version and Next Version Installed for each version of the firmware. However it only displays such information for recent versions/versions with cars, i.e. only considers current and one previous version of each car.
Break down by country/car/etc would be nice, too, but that is secondary.
Check e.g. https://imgur.com/a/QkuZf1J for examples.
The question I want to answer at this point is "how many vehicles were added to the beta in the last x months, so just implementing such a report might be easier, but it would be nice to have all the upgrade paths available. The database has the information, as if you click on any single vehicle, it has the whole history.
Customer support service by UserEcho