To be clear (and this is mentioned but not highlighted in the article), the previous Business plans were never guaranteed unlimited storage for orgs with fewer than 5 users ($60/month), the 1TB limit those orgs were supposed to have was just never enforced.
I was one of those users, and the thought that the storage limit could start being enforced at any time was always in the back of my mind. Now I'm on the Enterprise plan and can worry a bit less.