New mid-level content is always a hot topic, especially by people who are on their third or fourth trip to the well. We've all got those "If I never, ever, see this zone again, it's too soon" zones. The solution often bandied about is to create alternate progression paths so we never, ever, go back to Stranglethorn Vale. I'm going to put forth a different idea: Fix what is broken. This will help minimize unused zones, and maybe not spread out the lower-levels so new players can actually find groups.
Which seems to be the step Blizzard is taking with 2.3. In terms of quest progression and rewards, Blizzard hit it out of the park with TBC. You've got quest-givers nicely clumped together and often they all send you in the same direction. The cash, XP, and item rewards for completing the quests are excellent. When you compare the expansion quests against original Azeroth it becomes apparent how frustrating quests could be. It seemed like completing most of them involved long griffon rides for mediocre rewards. Quests felt like they were, well, I was going that way anyway...
I was originally disappointed TBC wasn't a true 1-70 expansion. I still am, actually; I'm not a big fan of developers tossing in a few low-level starting areas so they can put "fun for all levels" on the box. I'm not disappointed Wrath has no mid-levels -- this expansion is solely for high-leveled players. But the next expansion with new starting areas damn well better have new zones for all levels. In between expansions, though, I'd rather Blizzard focus their efforts on moving the game forward. Yes, I'm saying if Blizzard is going to spend time creating new areas, I want them to be for high levels.
Now, I'm not a raider. Not even close. Embarrassingly, the only raids I've gone on are "sympathy" raids where my guild felt bad I've never seen a given zone and we raid it. I've never set foot in Kara. So, yes, I'm proposing Blizzard spend time developing content I'm about likely to see as the Pope is to bless my keyboard. I feel the lack of new 20-60 content is a faux hot topic, and Blizzard needs keep some carrots ahead of the crowd that's chewing through them as fast as they can put them down. You have to keep the size of Blizzard's subscribers in mind – that "small number of subscribers" if counted on their own is a subscriber base most MMOs would kill to have. To date, no North American MMO has boasted a subscriber base even close to WoW's 10% mark of 900,000 -- at its highest EverQuest topped a little over 500k.
I will leave you to prove me wrong that the dearth of new mid-level zones is a faux hot topic. Be honest with me -- how likely are you to run an alt through new lowbie zones more than once or twice. How about through the new instances? Would you rather they put in new mid-level zones, or revamp old zones with new quests?