This is probably going to be a chore but i'm still going to raise it regardless.
Currently, almost all the epic dungeons are relic of tens of years ago.
During then, leveling is absolutely a chore ( however, with accomplishment ) and there is merit in getting party members to do epic dungeon raid because the equipments and even magic was much weaker.
If i were to contrast the newer epic dungeon such as Lost Bastilles and DeepWell Dungeon, against the older epic dungeon ( mostly lurking in the underdark ), the latter difficult is simply too easy.
I'm simply suggesting that rather than creating new dungeons, perhaps developers can revisit these old dungeons and make adjustment to their difficulty ( AB / AC / Saving Throws / AI ) or add new variety to it. Perhaps also extend a few portion out and spike the difficulty, at the sametime making better loots which deserves the merit of increasingly difficulty.
Two things to consider on what stop a SOLO player is, actually working dispels. Yes, dispel. If a dispel can reliably strip some by random of a level 30 PC. This dungeon can effectively stop 80% of the solo population base. However, better / increased loot matrix would be desirable for such.
The other will be true sight for those who simply enjoy Invisible raid.