I have seen all the videos and always watch the keynote releases, which is why I said it is a great little machine, but it could have been even better. (If you watch the videos, you will find the storage is a complaint in virtually all of them)
As to upgrades then it's like the Mac Studio with the storage plug-in (It just has 1 slot rather than the 2 in the Mac Studio), but better to get what you want at the outset, rather than upgrade later.

Bill