I think "pairing" has come to mean any number of people in a relationship in bandom - I've often seen writers put things like "Pairing: Frank/Gerard/Grant" in their headers :-)

It was almost nonexistent in popslash too. Which makes sense when you realise that both the first and second wave of bandom fans (in 2005 and 2007 respectively), were heavily populated by old popslash fans.