I was all for double XP weekend the first time it was announced...
I then realized that in order to get the most out of double XP weekend, the best way to do so is to simply grind since the double XP does not apply to quest XP. Travel times, quest research, waiting for spawns, etc is all non productive XP during double XP weekend... So not only does it lead players to mindless grinding, it also causes a big problem to quest/dungeon grouping since people just want to kill the most stuff possible in the shortest time possible.
In my experience, grinding is not a good thing to do at normal XP rate since the XP from quests makes it much faster to level.
So if they want to put another double XP weekend sure, no problem, but make it so it doesn't make people grind mindlessly to get the max out of it. Double quest XP would be a nice way to fix this.