While I still think the setting could be Dark Sun (or even something more out of left field), I do think DL is a strong contender for potential setting.
But the races to have a bad rap.
I share this sentiment, but I would totally trust the 4e team to be able to keep those races fun and comical WITHOUT having them be pure comic relief. The reason is three-fold: Solid DM advice combined with "open to interpretation" mechanics and a desire to fix what is wrong.
There's no real reason that 4e's halflings and kender can't be each other. The kleptomaniac kender stereotype (like a lot of these comic relief stereotypes) is a
player problem, not a
race problem, and there's no reason that a 4e DL couldn't play up the "curious, bold, adventurous" angle and downplay the "no sense of personal property" angle (or even mostly remove it entirely: "Kender aren't idiots and they learn how to avoid annoying other adventuring companions quickly, or they die.") Combine this with solid DM advice for handling comedy and inter-party conflict in the game (which any DL DM's guide would be remiss in not including), and you have a recepie that fixes that kleptomania problem.
Tinker gnomes hurting themselves and gully dwarves being unlovable can be flavor without any mechanical support. "Oh, your Tinker Gnome artificer uses an invention that works well enough to activate the power and also leaves you covered in slime and oil" doesn't need any mechanical ramifications. Gully dwarves don't need negative ability score modifiers: if they're NPC's exclusively, it can mostly be dealt with in flavor text and art. If they can be PC's, well, same thing.

PC's also have the "I'm a hero, I don't have to be lame" justification, and buttmonkey status can always be reinforced through the racial powers or somesuch.
The 4e team is very good at knocking things down and building them back up anew. The new form isn't always very pleasing to everyone, but DL would have the advantage that the "new form" has no reason to be different from the "old form," aside from getting rid of some of the more obnoxious player problems. Noble Draconians? Kender-halflings? All of this is cakewalk.
Blaming Kender for being a jerk is like blaming the Chaotic Neutral alignment for...well, being a jerk.
And we can stop barking up the "orders of magic = classes" tree. Why would they need to limit it based on class? Why not just keep it purely alignment based? Warlocks can be LG just as easily as paladins can in 4e. Any "arcane power source" could count for it. Why not have black robed enemies be able to call on the powers of a Bard, Sorcerer, Wizard, Warlock, and Swordmage?