I guess if you are going to take a hit on the enthusiasts by offering a 1TB tier, then you might as well just go all the way. Microsoft has been rolling out an unlimited tier to their various subscription products, starting with Office 365 Home, Personal, and University. OneDrive for Business customers, who are currently limited to 1TB of total storage, will be granted the unlimited tier, starting with "First Release" customers in 2015. It will probably arrive to "Standard Release" customers a couple of weeks later.
The 1TB tier was not around too long. It launched to several different subscriptions in late April, starting at $5 per user per month. Now, the current cheapest option is $7 per user per month, but it comes with a license of Office 365 Personal. Note that the first three tiers, Home, Personal, and University, are each non-commercial licenses. The rapid increase in capacity could mean either that the original initiative was very successful at wooing new customers, or the exact opposite of that. It is even possible that unlimited was the original intent, but they arrived there by way of a 1TB plan, either to shake up competitors, to double-up on media attention, or simply to dip a toe in. Basically, they could have done this for any reason under the sun. We have no idea.
Unlimited storage in OneDrive for Office 365 Personal, Home, and University is currently available, starting at $7 per user per month. OneDrive for Business customers will need to wait until 2015.