Something like this sounds about right.
It's getting a bit ridiculous when for the last 2+ years Apple sells devices with lots of internal storage (MBPs: 8TB, iPads: 2TB, and now iPhones: 1TB), yet the max iCloud+ they're offering is 4TB (as an upset to get people on their One sub (provided you live int he three countries that offer the top plan (due to News app being limited) – but what happens if you want 6TB or 8TB (or more)?
Remember, you've got to use the current 2 or 4TB limits for many things here: your iCloud Drive file storage, plus iDevice backups, plus iCloud Mail, plus apps that use it for their storage. That all add-up.
And while we're at it, I'd like to see Apple remove the 100K track limit in Music (both AM subs and iTunes Match subs) too for your own tracks... I have 98K tracks I own, and am going to be artificially restricted when I hit 100K, just to annoy me. Why not just get us to pay you Apple for the extra above this, instead of completely blocking Apple Music device sync when we hit the limit?? Frustrating.