They could make 40 man PvE scenarios, to work similar to world bosses; but to be more scenario-like rather than a single boss (even if he has adds). Off the top of my head:
Alterac Valley as a PvE 40 man scenario - essentially it is similar to the old AV, but with waves of horde NPCs spawning rather than horde players BUT WAIT. The objectives are all there, with the old Lieutenants as mini-bosses; but worked out much more like a proper MINI boss, so several abilities, maybe multiple phases, but something that can be done by about 15 people without too much trouble. These Lietenants buff the FWK Lieutenants + Drek with buffs as long as they are alive. You have to kill "Galvangar" and cap the first 2 towers. After first 2 bosses you progress further south, do the same with the FWK towers. Capping a GY stops the NPC waves spawning at that GY. Capping the mines buffs allied NPCs. Killing Drek'Thar is the final part of the encounter. BUT THERES MORE.
As soon as you engage the 2 Lieutenants "assassins" will periodically spawn to attack our Lieutenants and Balinda, and will need to be taken care of. If our Lieutenants die the assassins start spawning in Dun Baldar. If *those* Lieutenants are killed, the assassins will cap the Aid sation and NPC waves will beign to assault Vandaar.
The final rewards are there for killing Drek'Thar, comparable to the world boss of that tier (say 559 for this tier) There is, however, also a timer, and the faster you complete the encounter, coupled with how perfectly you complete it (no of allied deaths, no. of allied Lieutenants still alive etc.) will also reward bonus rewards, up to and including bonus loot bags for perfect completion (and fast) to bonus valor, satchels of exotic mysteries, VP etc.
So whilst this will be "puggable" to maximise the rewards you will want a relatively organised group and strategy, with assigned players to take care of the assassins spawning; groups assigned to take down each mini boss at the same time and also players free to keep back the waves of NPCs; maybe some assigned to venture further to early cap graveyards, or cap the mines to buff our NPCs... As the groups would be relatively spread out, the lag shouldn't be such a horrendous issue. I'd love to rock something along those lines. I merely used Alterac Valley as an easy referenced example; there could be so many EPIC encounters to make in such a format.
*Disclaimer: Potentially