Personally, any game as a service is a temporary fad, every expansion is a temporary fad... just depends on how you look at it.anything classic imo is a temporary fad
I'm not really sure twinks (with popping queues) exist outside of wrath and retail. I'm sure there's some on Warmane but eh.player base is greatly diminished plus they are scattered in multiple classic versions, retail, and private servers.
That being said, everything that is classic is cross server, even grouping up cross server to queue bgs is possible now.