They "tolerated" a non-compliant use of their service for so long time (maybe because in the past their only goal was to increase adoption?!?) and suddenly they decided to change strategy?! No problem, it's their choice, but adding an x days grace period should be the standard. It's really easy to do.
> Would it be nice for CF to give a heads up?
Well yes, it will be really welcome. Mostly for all other their user(1/3 of internet or something like this) that maybe doesn't even know there are not full-compliant to TOS and risk their business to be terminated suddenly.