Depends on the type of single player content... I like the social aspect of WoW – I just don’t like to raid with other people. I like doing dungeons, battlegrounds, questing – well, even fishing with other people. I love guilds, chatting in-game and the auction house. So I’m not saying that I want to play WoW by myself, I’m just saying that I don’t like to R-A-I-D with other people.
What I would like to see is more ways outside of group raiding to get good gear. When I first beat Kanrethad (4th try, patch 5.3 with VERY crappy gear, 463 iirc), not even one of my heroic raiding friends had done so. 5.3 Kanrethad was a fight full of precise, clockwork mechanics. If your position was wrong by a hair, you died. If you didn’t pay attention, adiós. If you don’t react to mechanics asap, wipe. If you didn’t know every damn thing about your class - try again, son.
So make very difficult solo scenarios with high ilvl gear rewards, and I'd be happy with it. If people chose to raid in a group, great, more power to them. No need to change that. But give solo'ers the option.
I just can't stand loot drama, people whining because the dps was low, healer didn't heal, tank didn't have a clue... Tight schedules, kissing ass to get a raid spot, GM favorites, all that stuff.