No Unique doesn't. A big problem gnomes have is that their niches are neither conflicting nor contrasting but are basically unique.
Halflings drift more easily than gnomes because what they are is something other than a grab bag of tropes thrown together without thematic coherence. And that is why as of 2017 they were more popular than gnomes in every single class except wizard, druid, and by the thinnest of margins, warlocks.
Are we really sure that isn't because Halflings have what is by and away one of the most powerful traits in Lucky? Are people rolling halflings because they like Halflings, or are they rolling halflings because Lucky is one of the most powerful skills in the game?
Meanwhile gnomes are hodgepodged into their role of "like halflings but with random subrace-determined magic". Which is why halflings are more popular in every class except the ones where the random magic hits the class on the nail and, by the narrowest margin, warlocks.
Halflings have an identity. Gnomes have gimmicks.
Look, if Gnomes are anything, its "Like elves but small" or "Like dwarves but magical". Dwarves and Elves are the go-tos when it comes to Gnomes, not Halflings. Halflings are agile and either sneak-thieves or hobbits, with no inbetween
The Halfling identity has been "Hey, remember this popular book? We're just doing that and adding nothing (Except Eberron and Athas who did a complete 180 from how Halflings were because they wanted to do something, anything with them other than just hobbits again, and even Eberron couldn't escape that entirely)
There are reasons elves get complained about.
But you can't deny their three main sub-races are each a visually and stylistically unique one with its own niche. You'd never confuse a drow for a high elf, or a wood elf for a drow.
It has always only been burrowing mammals.
Races of Faerun, Forest Gnomes get Speak with Animals as a SLA. No restrictions on size or type, just flat Speak with Animals.
Just halflings with a completely different gimmick from being able to talk to animals. And this is why gnomes as a race in 5e are a failure. The ones who play Dr Doolittle are basically entirely unrelated to the fiddlers.
If you wanted a coherent theme between the two rather than to make a grab bag of unrelated tropes and pass it off as a race you'd give the rock/tinker gnomes psychometry and as such able to listen to objects. Forest gnomes communicate with animals, rock gnomes with objects. Very different uses coming from the same place.
The only loose connecting thread between the types of elves is "Good at magic", "Agile" and "Lives a long time". The ones who worship demons underground are basically entirely unrelated to the forest dwellers.
When the go to example on how to make a varied group of subraces that have stood the test of time and keep coming back barely has thematic consistency, is it really a requirement for it to be a thing? Do we want subraces to be distinct, or basically identical? I'd argue we want distinct. Remember, no one cared about Githzerai when they were just "Githyanki but neutral", it wasn't until Planescape: Torment came along and gave them their own thing that they came into the limelight
And not a thing of value is lost. Because gnomes are not a race, they are tropes shoehorned into a race that is only there because it has been there from the start and changes every edition from one unpopular choice to another, never really finding an identity between gnomes and dwarves.
Every race except humans in this game is tropes. And let's not get started on dwarves because as far as tropes go, dwarves are just a trope. Folks always try to make elves different, but dwarves are always just the same "Grumpy bearded Scotsman" with no changes to that one single worn trope, ever. If we're judging gnomes for being a collection of tropes, what should that say about races who never change from one singular identity, or are too tied to other stuff?
We gain less space taken up and the ability to include e.g. goblins. What do we gain by keeping them? What do they actually do that halflings or goblins don't?
A small Fey race that hits those niches the halfling can't, because Halflings are 'the small everyman' per everyone's descriptor of them and too tied to Tolkein to go into little people mythology that elves have left behind, and gnomes embrace. Frankly they should embrace it more, but I've had this "D&D didn't touch fey stuff enough until 4E and suffered for it" theory going for years
Indeed. They have substance. They leave pure gimmickry to the gnomes. Of course you could mix the two by making gnomes halfling subraces.
Their substance is "They're all farmers and like cushy lives". That was.... Basically half the backstory of my fire genasi (The other half is that he's adopeted, doesn't know who his actual parents were and has horrid nightmares of someone trying to escape from the plane of fire, but that's probably fine, probably). Is that really something we can say isn't a gimmick? Because, frankly, its sounding like Halflings have only ever had one gimmick and that gimmick is "You're a hobbit from Middle Earth"
See, I'd argue that gnomes are actually the anti-halfling. Halflings are the everyman of everymen. Even among other races, they're the ones expected to be the most down to earth, eternally tied to the portrayal of Hobbits of Lord of the Rings. They're the people who just go on an adventure before retiring after the fact, once their blade and soul is stained enough with blood. They are mundane, that's the power of halflings. They are as mundane as possible in this magical world.
Gnomes, on the other hand, are the opposite of this. Even the most basic of them comes from people who talk to animals on the regular, invent spectacular machines, or live and thrive in one of the most hostile places in existence. They've all of the magic elves do, but without the aloofness that comes with their taller cousins. They are the opposite of mundane, seeped in magic, mystery, a stranger world. They embrace the wilder side of it.
Merging the two together is a disservice to both of their identities. You're determining that the halfling's mundanity should be destroyed, or the gnome's embrace of the other side.
Is there really much support to keep the game's least popular core race?
Just as something has to be the most popular, by definition, something must be the least popular. Removing something just results in something else getting that label, like Half-Orcs Plus, well, by that theory.... We'd have removed other stuff long ago. Gnomes were infamous back in 3E for being able to easily get Shadowcaster, so going off that theory, I'd say Halflings would have been more chopped due to how 3E handled things.
And there's nothing to lose here. This is the problem.
Except just, pissing off the people who do like gnomes. Like, let's not forget how absolutely vicious the Warlord debates get here. Sure, gnomes aren't the most popular, but they've a dedicated fanbase who will come out
Don't forget, there's plenty of people decrying the 5E decision to make Gnolls unplayable and Designated Evil Race. And gnolls are far worse than gnomes in identity issues. If random hyena mooks get that attention, then what would a race that's been its own for the vast majority of the game's lifecycle going to do? Plus see also the pushback on Shadar'Kai becoming an elf subrace, despite Shadar'Kai starting as fey
Below gnomes nowerdays, based on more recent stuff I can find.