Tserrina has been "building an army to destroy Norrath" for a looong time (the lore is Velious --3rd expac). Yes they have twice done ToFS with anniversary stuff. That's not what I am saying... I want a world event where Tserrina's minions are all over the place and ranging from level 1-100 depending on the zone they are in.
Fast respawns, highly social. All the mob types from ToFS. Floor bosses as world bosses.
Even if this event was staged in Hole-paineel-tox (warrens would be fun...) as the reentry point of her invasion it could be fun.
Toxxulia Forest= level 1-20
Paineel= (I would do city as well, but that's not precedented...) newb area to the Hole could be level 20-40, there is enough real estate if it was filled up with mobs in all the halls
Warrens= level 40-80 (big enough with enough separate areas to keep it packed full, have Tserrina's minions killing the kobolds too)
The Hole= level 80-100