Seriously, I've yet to see anyone offer a reasonable explanation of why it would be bad if the dray were dragonborn, or why it would be bad to include tieflings, other than "Well, they weren't there before!" If such things are added in without any effort at making them fit the mood, theme, and feel of Dark Sun, then yes, that would be a bad thing. But if they're included in a way that fits, where's the downside?
It's not necessary?
Yes there are some 4e fans that were also Dark Sun fans. I'm not saying you don't exist. I'm saying you're rare - VERY rare - to the point of being potentially statistically insignificant (NOT SAYING THAT AS AN INSULT).
Why do people >:| at dragonborn and tieflings? Because it's an unnecessary change. Literally, it's a change that is 100% not needed.
This is why 4e and Dark Sun have such a clash. 4e is 100% "Everything is core, use everything, a kitchen sink in every already existing kitchen sink."
Dark Sun is the exact polar opposite of this.
On top of that, there's also the worry of fluff carried over. Instead of dragonborn being altered to fit the dray, it'll be the other way around - that dray will be altered to fit the dragonborn.