I also want to see them more than I want to see any other race Uska, but the way I see it Shifters will actually be way tougher to do than druids or frankly any other race have been to date. Doesn't mean I don't think Shifters would be a better addition than Tieflings, but I can't see it being anything other than massively labour intensive.
This is specifically because they don't change as radically as druids do.
The similarity between druids and shifters end at the tech developed to enable this:'when player pushes this button change these stats, apply this animation and replace player sprite with this model'.
Druids:
Wolves, bears and elementals all already existed in game. Animating the transformation and new attack sequences was the main challenge I think. But weapons, armour cosmetics, spell cast animations and all that aren't really a concern - most things either are hidden within the body or just plain aren't possible in the alternative forms.
Shifters:
Shifters have a second humanoid form. You might base their main form on humans, but shifters still need an entire set of racial animations doing for wearing gear, swinging weapons, casting spells and so on, plus a transformation animation. That's before you even get to the crunchy things like stats and enhancement trees.
So I can see why they'd want to do Tieflings next!
Tieflings:
Have a basic skin that can be reused. They need to do something with Helms & Character skins, possibly armour if they do tails but other than that can basically reuse existing models with some fine tuning of features for the character gen screen.
Aasimar:
reuse the existing human skin or possibly the elf one but without the pointy ears. So really should be very easy. As for reasons for having them at all - some people are clearly interested for reasons beyond the +Wis. Those reasons should be considered valid. Also, Aasimar are the other side of the same coin. If you're doing Tieflings, you really should do Aasimar. It would be like introducing Half Orcs without Half Elves.
Racial look and feel for Tieflings and Aasimar
For Tieflings and Aasimar the conversation about racial features is where the extra time might come in: they're both essentially halfbreeds, like Horcs and Helves. In both cases the 'distinctive racial features' appear on a spectrum - they are not fully expressed in all cases, and many of them don't necessarily appear at all on a given specimen.
Some tieflings, for example may have no distinguishing features except the eyes. Or very small horns, or a tail small enough to go inside clothes. Aasimar might have weird skin tones and oddly lustrous hair or maybe oddly compelling eyes... but they also may not have any of those things.
4th ed is where they locked everything in place and exaggerated all the features to always be present and prominent - essentially yet another retcon in the name of their blasted drive for 'streamlining', which just gutted the game completely.
My view is that the 'half breeds have weird mutations' thing that used to be core to DnD wherever you found them should be reflected at character creation in DDO - e.g.:
Tieflings
should be able to choose either Tails OR Horns, and should have the option to have both, but it should not be forced upon them. Horns and tails should have a few different looks, but no need to go crazy - think like adding scars to the face in terms of the number of necessary variations.
Aasimar
Their only outwardly manifested 'mutations' seems to be their propensity for odd skin and hair colours - so throw in some wierdness and new hairstyles, copy paste human or maybe elf without the pointy ears, and you could call it done. But note Aasimars often - not sometimes, often - pass themselves off for human for long periods and work in high places in society to 'do good' - so for Aasimar it should actually be possible to create one that is very close to 'normal' looking.