I've never actually known business requirements ahead of time, when I worked for a startup and for a large company. You build your schema iteratively and yes, accept some temporary bloat when cols get added thoughtlessly.

The UUID backup/recovery thing isn't an issue if you're doing append-only. Joins on UUIDs are far slower, enough that even at small scale it can cause issues when you have many joins. Anyway I won't argue too hard against UUIDs cause they work too, just anything is better than using meaningful fields as the PKs.