What did Lord Blackburn mean by "long-continued action" in 1884?
I would take it to have a meaning in keeping with 5. Specifically, I take his comment about "no such long-continued action" to mean that the cause of action (i.e., the specific kind of breach of contract) that was relied on in the present case had not been brought before the courts, or relied on in court, in the recent past. Given that it had not been recently considered, and previous doctrine had not recently been relied on, it was open to the present court to reconsider it. That is in keeping with the double-negative of "no action ... to render it improper ..."