I think Metcalfe’s law could be clarified as “a network’s value increases in proportion to the square of its active participants” rather than simply nodes. Although Facebook has over 2 billion members (nodes), the more important metric for them is their monthly active users (MAU).
Re-orienting our focus towards “active participants” as the primary value metric paints an even more precarious position for established networks, as their value can rise and fall monthly or daily depending on participation. A “Metcalfe-Hall Equilibrium” is more unstable when measured in terms of MAU than nodes.
Although I may still have a long-lost MySpace account linked to an abandoned email address, that node is effectively worthless, just as my Facebook node could be worthless next month if I were spend my attention elsewhere.