Currently, STABLE allows sending of STABLE messages to all members, or to the coordinator only. The latter is controlled by attribute send_stable_msgs_to_coord_only (default: true).
Sending STABLE messages to all members means that all members have to maintain digests, plus requires the StabilityTask to be able to stagger STABILITY messages.
Since sending STABLE messages has been the default for a couple of years now, making it the only choice makes sense. In addition, this allows us to remove some code and thus simplify the code.