If anybody wanted to bother they probably could hold them to it. They didn't really mention whether the existing accounts were grandfathered in. If not then it was rather dishonest of them to promote "free forever." They could have just said "free" instead.
I plan to sue them after the universe ends, as that is before "forever".
I imagine that current holders of the plan would be grandfathered.
the impression I got was that they are just no longer offering the free plan. If you signed up when it was free, you are good. Otherwise, you have to pay now