Nothing happened to it, really.  Before Guildfall it was the least inhabited area and still seems to be. It's a specialized area,unlike the main three so.its going to have fewer people in it anyway. 

However Arenas in RPing are fairly popular. They even used to hold a massive every other year tournament(Grand Tournament), in which people from all kinds of sites would compete - including a couple of our current/old members(Skallagrim, for example). They also have a site where you can get ranked in a list of fighters(I'm listed there as well, though some BS kept me from being ranked higher).

The Arena also held Guild's only working multiverse for a while.