ControllerApplication "acknowledge" subscriptions are not used - unfinished feature?

[grant-allan-ctct]

The ControllerApplication defines a list of subscribers _subscribers_acknowledge on this line.

As things stand, someone may add to this list using subscribe_acknowledge here. The unsubscribe_acknowledge function here is publicly available too, but it has no code in it. (I.e. once a subscriber is added, it can never actually be removed.)

But no code anywhere does anything with the items that anyone may add into this _subscribers_acknowledge list.

I am not sure of the intent. Should we try to finish/fix it, or is it better to just delete it to save confusion?

Maybe the intent is that someone can subscribe in order to catch the acknowledge message (0xE800) that a device on the bus might send us if, for example, we commanded it to change its source address?

Another interesting thing related to message acknowledgement is that (private) function __send_acknowledgement in the J1939_21 class here is never called. I wonder if these two items of uncalled code are both related to an unfinished feature?