And what does it gain us? A whole bunch of people complaining that since they don't use the Nentir Vale... then how do all the other goblins behave?
That's actually part of the positive effect here: it helps people think about the goblins that they WANT to use.
If they just want to use some statblocks, sure, fine, Nentir Vale goblins are as good as any, they'll go for it. It meets the needs of the folks who just want a frickin' goblin. No reason NOT to use them, really.
If they want to put more thought into their encounter, they'll think about how they might tweak the Nentir Vale goblins to be the goblins in their own game. Maybe it's just RPing them differently, maybe it's a re-skin, maybe they'll steal goblins from Harry Potter, whatever. So it meets the needs of the homebrewer by being clear that these goblins aren't the only kind of goblin out there.
It also jigsaws into other elements of the D&D experience. If someone really likes the goblins from Dragonlance, maybe when they later see "The halflings of Krynn are called Kender..." they'll start thinking that Dragonlance is something they're interested in maybe digging deeper into -- que the novels, the movies, the campaign setting, the board game... So it meets the needs of the setting fan by roping more people into the setting by giving them digestible breadcrumbs of interesting lore.
It also encourages DMs to steal ideas, which is what they're doing anyway. Maybe you don't use anything from the Nentir Vale except for the stupid goblins -- congrats, you engaged in the time-honored D&D tradition of stealing liberally from others, as just like Gary! So it meets the needs of anyone who just likes those particular goblins, too.
About the only people who might stumble on those references are people who see those words and just
shut down, and refuse to read any further, somehow convinced that nothing that involves the Nentir Vale could ever appeal to them. And those folks are basically just shooting themselves in the foot -- if they want to then cry about how that monster entry is useless for them, because they don't play in the Nentir Vale, they're ignoring the fact that they don't play in Middle-Earth and yet, here's a dwarf and and elf and a halfling. Those criticisms, essentially, aren't really about not being able to use the monster, they're about the bias of the reader, and those folks ain't gonna be happy with any creature that doesn't appeal to them personally anyway.
*Plus* you get a whole bunch of people complaining that obviously WotC thinks the Nentir Vale is the default setting of D&D because why else would they describe these specific goblins instead of a more generic one?
There is no such thing as a generic goblin. There are only specific goblins that acknowledge the fact that they're specific, and specific goblins who try to be everyone's specific goblin.
And this particular objection is dodged quite nicely by the page next to
Goblin, which is maybe, I dunno,
Gibbering Mouther and it begins with the sentence, "In the Underdark below Waterdeep...."
So monster entries reference many different settings, because those are ALL part of D&D.
So you haven't GAINED anything. You still have whole masses of people using their own descriptions of goblins for their own settings. All you've done is hold the hand of the poor soul who just somehow is unable to grasp that what is written in any book is not a hard and fast rule, and that they can adapt anything they read as they see fit.
You've gained much of what I've laid out above -- four different kinds of players with competing, often mutually-exclusive interests, have their needs met by this idea. Furthermore, it enhances D&D's reputation as a game of imagination that gives you the power to play your own fantasy worlds with your friends, and diminishes the heavy-handed branding that tries too hard to define what a million different tables define for themselves anyway.
I'd rather give my fellow players a little more credit than that.
And yet, you're not willing to give them credit for being able to look at a cool monster entry and say "I'm going to use
that!" regardless of the fact that it references the Flanaess?
Weird.
Do you REALLY believe there's room? That there will ever be room? That when given the choice between using page space in a MM to include Description and Ecology *or* Two Descriptions, that someone at WotC will actually go with the dual scrips? Or do you instead just keep rolling this d1000 over and over and over again on the minute chance someone at WotC will finally see things the way you see it?
Depends on the priorities of the publisher, really.
And for me personally, it's less about if WotC embraces the idea, and more about identifying the strengths and weaknesses of this idea by talking about it.