I think eventually I'll get one of these, but not for a while. I'll use my current 4TB external HDD.
I'm hoping, and sort of suspect, that Microsoft will provide a software solution for game storage with external drives in a future release. A "Smart Storage" setting or something, where games that you haven't played in ~90 days or something, or that you're unlikely to play, get moved off of the internal storage once that storage becomes, say, less than 25% free space... Like you get a prompt:
"Your Internal SSD is at 25% storage capacity, Xbox Smart Storage can move recently unplayed games to your external hard drive. Proceed?" You click "ok," and then it goes ahead and does it ... ideally in the background.
Later, if you ever want to go play a game that is on the external HDD, it tells you "Xbox Smart Storage has to move this game to your internal SSD to play, this will take a few minutes but you can use your Xbox in the meantime," or something, and it moves it for you.
It seems like a common-sense enough feature that I assume they have it as a feature development in the pipe.