The only signs of decay of bodies in OB were rarely you'll have a quest and find a zombie with an actual name, not just "zombie". I think it would be cool to have a skeleton model for each creature, race and gender. It seemed very odd to have murdered someone in OB and come back a year later and the body hasn't changed a bit. I'd like to at least see the clothes be mostly torn apart from animals trying to eat the corpse, I'd like to see maybe flies swarming around the body and just a basic body decay over time. Point is: make it more realistic and not like OB where it looks like a guy is alive and napping for eternity.
Oh wow, that's a good way to have a lot less people working for Bethesda. Morbidity aside, that would take a tone of CG and scripting work. Such realism sounds cool, but your talking a lot of overtime. Any Dev who is reading this is likely already on his 5th pot of coffee today as is.
2nd opinion: Now that I think about it, why not just have the body disappear when you're not around. If the body is located in a city, we can say the guards have been notified and took care of this. And we can also find a new tombstone with the name of the victim on it. Or if the body is in the wilderness, we can just say some animals took it home for dinner.
Who's to say that's not what happened anyway?
Actually if anything the bodies need to disappear faster in these games. On of the reasons that caused all the slowdown and freeze ups in Fallout 3, was that the bodies hung around for a long time, which added addition lag to the gaming world. This is why it was advised to dispose of every body in Morrowind and close every door after you opened it.