I think it violates the spirit of what the Nentir Vale was created to be: a generally undefined place to just "drop stuff" so that while it has a name and a loose geography, it's got a lot of empty space for DMs to work with. And also a place for the designers to just say "It's set in the Nentir Vale".
By making a Gazeteer, it's no longer that; it's spelling out where All The Stuff Is. And the Gazeteer is probably going to be "Here is where all our future products fit in". It's gone from a Points of Light skeleton to a fully fleshed out, mapped region with all its blanks penciled in.