I can't believe anyone could seriously suggest that this is why there are no raids. Raids, being instances, can be set anywhere. Apart from perhaps the Watcher, none of LotRO's past raids have been especially lore-appropriate.
The current raid tier in WoW is mostly set in the *starter zone* for one of the factions (basically in the equivalent of Bree).
Just to go down the list:
1) A raid could be set in Bree, or even in the Shire. By this part in the story, both are in trouble.
2) A raid could be set in Angmar. No more or less lore-appropriate than the original Rift raid, which was invented out of whole cloth.
3) A raid could be set in the Misty Mountains near Rivendell. No more or less lore-appropriate than the original Helegrod, which was invented out of whole cloth.
4) A raid could be set in Moria. Dorfs are constantly doing stupid things and getting their fat butts kicked by something.
5) A raid could be set in Dol Guldur. It is still an extremely important, and active (in the lore) base of the enemy.
6) A raid could be set (primarily) outdoors almost anywhere in Rohan, as a commando-style strike on an army camp of Saruman's. Maybe they are bringing some deadly artifact or other dwimmer-crafty contrivance that will massacre the Rohirrim unless destroyed. Maybe Saruman has recruited or genetically engineered a particularly powerful lieutenant to command his forces in the field. Maybe there's a force of Rohirrim under siege who need to be rescued.
7) A raid could be set in Dunland. Like the previous option, it would easily tie into the military situation, and Dunland is a blank slate as far as lore is concerned, so there could be a fortress, or military garrison, or even some older ruins.
8) You said it yourself: Paths of the Dead and/or Glittering Caves. The latter would a great choice to showcase the art team's work, as they are described as breaktaking in the lore. Paths of the Dead can be the following tier, once the story reaches them.
9) A raid could be set in the Ettenmoors. Still plenty of bad guys there.
10) A raid could be set literally anywhere else in Middle Earth. They already have the precedent of going to completely random places (Erebor) that have no connection to current expansion. So pretty much anywhere in Middle Earth except maybe Gondor or Mordor (if you consider those "reserved" for future content) could be the setting for a raid. Rhun or somewhere else the Easterlings control would be a possibility. Again - total blank slate lore-wise. The Lone Lands, Trollshaws, Evendim, Forochel, North Downs, Eregion - all plenty of possibilities too.