Imagine all group content (scenarios, dungeons, raids) to have the option to be soloable. Bosses would have a solo setting, you'd go in and kill them, a la Diablo 3 - if you learn the mechanics then you beat the boss by yourself.
-no more 30-40 min queues for dps
-no more dealing with certain....personality types. Or having to rely on others period for that matter...
-same progression on gear/content as regular group content
-gear a couple ilvls below LFR gear.
-bosses would have lower HP and do less damage for obvious reasons.
-certain raids would have faction NPCs to help. Ex: Heart of Fear to have Klaxxi NPCs to join you in battle.
I generally prefer playing solo in PVE, but you'd have to take out most interesting mechanics to support a solo experience. The monk "training" quests are cool and have mini boss-like mechanics so you can practice your various abilities, but they only work because they're class specific. I wouldn't mind dungeons having a duo/trio mode though, but I guess that's really nothing but a scenario. If only you could play those solo or duo...