I have an idea for less popular events:
What about making it so, that if you dont get matched after 3 minutes, you automatically enter an empty arena with the cache having a 5 minute timer on it? Just like the old proving grounds. Then people would enter just because they think they can get free loot from it and thus increasing the chance of a fight.
I know this matchmaking system brings back the first come is first to get the fight like the old arenas(which still need to come back or get replaced by the system I posted here), but sitting in queue for hours without getting matched up sucks.