Purchased and supported Vista Social here from AppSumo that initially included 𝕏 posting.
Seems it was acceptable under AppSumo’s terms and Vista Social themselves figured it was a wise decision to remove features and functionality from AppSumo users that supported their platform.

Not even sure how this was possibly acceptable by either party, selling promised features for the lifetime of the product; then, removing them and converting them into “add-ons” for a monthly subscription fee?