How detailed are we asking though? Would a description of Gruumsh orcs in NV2 followed by a "In Eberron, orcs are druidic mystics who fight aberrations" paragraph work? Because that's basically what we have now and I got the impression it doesn't.There's a third possibility--one that D&D has actually done in the past. In some of the 3x MMs, the monsters (or at least some of them) would have two sections at the end of each write-up, entitled "Monster in the Forgotten Realms" and "Monster in Eberron."
It seems that WotC could go back to something like that, if they had a "Nentir Vale 2.0." Here's how the monster is generically. Here's the role it plays in this particular setting. It would be particularly useful if those two sections were sometimes quite different, as opposed to "here's gnolls, who are violent ravagers, and here's gnolls in NV2, who are violent ravagers in this particular area." More like "Gnolls are territorial hunters but are willing to let intruders alone if they prove they aren't going to hunt the gnolls' food supplies. In NV2, they are actually demon-spawn who will kill anyone who enters their territory."