Something else I failed to notice: step 2 of the algorithm to monitor the list of available presentation displays instructs the user agent to "retrieve available presentation displays" with a link back to the definition of available presentation display.

However, at this stage, there is no URL against which availability can be determined, the goal is rather to retrieve a flat list of presentation displays. Next steps (3.3.1 in particular) determine whether these displays are available for URLs in the set of presentation availability objects.

In other words, I think we need to drop "available" and rather link back to presentation display.