the unlimited plan was phased 7 months ago [0] so got few notices, with the final one 7 days before termination. so the guy with 250tb of data neglected that for half a year and now is surprised.
The thread you link to above says “People using anywhere from 5.??TB all the way to 152TB … got the email” but I assume that email is the one already mentioned which states large accounts are going read-only.