@Solid:
I believe it's Tamas fruit for many reasons.
The devil fruit in question would have been talked about when the gurosei heard the report of Zunesha.
Zunesha is over a thousand years old, a walking relic from the past, who coincidentally was ordered to roam the seas for an eternity, and could not stop doing so even in the threat of dying and taking all of it's inhabitants with it, meaning even if it wanted to there is something unnatural that blocks his will to act.
With Zunesha being a living legend, it is not too far off to think that the devil fruit that once controlled is also a legend, probably they're linked together from the blank century. Since the WG can not erase a devil fruit that they don't know the whereabouts for, they decided to change its name to make it forgotten, so even if someone would stumble upon it, they would not know it is the fruit from the legend that could control a massive beast like Zunesha.
The fake name is kibi kibi no mi, the millet fruit. Compared to other devil fruits which has a food theme something sticks out with the kibi kibi no mi. Tama herself said that her dumplings provides no nutritional value, unlike the fruits of lets says Mochi or Biscuit that actually produces real edible food. How could millet not contain any nutrions?
There is also the instance of where Luffy and Tama compares her dangos to the mochi in oshiruko, but millet is not mochi, mochi is made of rice not millet. I think both these points could contradict that Tama is producing millet.
The gurosei is probably not even aware of Tamas existence, they just assumed that her devil fruit has emerged again due to the arrival of Zunesha, and this would make even more sense if the former user of her fruit was also from Wano, most likely a Kozuki that would put in a clause in Zuneshas punishment that only a Kozuki would be able to break the order.
So how would Zunesha be able to communicate with Momo? Due to VOAT, assuming VOAT is a form of haki, it is known to bypass devil fruit abilities, and Zunesha was allowed to reach out to Momo because he is a Kozuki and because the situation was a life or death situation he did so with Momo, and not with Oden when Oden visited Zou for example.
So why would Tamas fruit of all fruits never have emerged for hundreds of years? That also regards to the Kozuki, after the death of the former user the fruit have been kept safe and hidden for centuries, and eventually probably even the Kozuki started to doubt its powers, and it just became one of many treasures kept safe by the clan, until Tama ate it. Given that it is like 99% certainty that Hitetsu is actually Sukiyaki, it's not hard to see either how she would come in contact with it, the fruit along with Oden swords (and perhaps even the road poneglyph) were things that Sukiyaki were keeping safe, after he threw away his name and devoted himself for his role as Hitetsu, Sunachi!
So who exactly is the former user, what is the fruits real name and why is it a legend?….
The former user as specified before should be a Kozuki, and since he was in contact with Zunesha I'd also assume he is the one that made the moon warriors of the mink tribe devote their allegiance to the Kozukis, in the legends he was known as the Moon God insert forename Kozuki and he lived during the blank century. With his devil fruit he could produce tsukimi dangos, moon viewing dangos, that are meant to look specifically like the moon itself.
https://en.wikipedia.org/wiki/Tsukimi
https://i.imgur.com/ygBmS1b.png
these dumplings are also referenced in Enels cover story
https://onepiece.fandom.com/wiki/Enel%27s_Great_Space_Operations?file=Chapter_450.png And the real name of the devil fruit would be… Tsuki Tsuki no mi, the moon fruit.
This is a Solid (heh) theory allright and i can perfectly see it being correct in the end.
There's only one missing link in my opinion, and that's how the Elders would make the connection of Zunesha arriving near Wano and the fruit being active or awakened.
We know for a fact that Tama never had anything to do with Zunesha, so even if we assume that it obeys to Momo because of the order it was given by the original user of the kibi/moon fruit, it's still that user's power that would be in effect. If that same order is what compels the elephant to roam endlessly, the top dogs of the WG would now for sure that the ability itself was still effective non-stop for the last millennium or so, and shouldn't be surprised that it's "reappearing" now. Again, we know for sure that Zunesha being there has nothing to do with Tama and possibly everything to do with Momo, and their connection has no known bond with devil fruits.
All that is assuming the five elders are reacting to the report of zunesh arriving, which again i don't believe to be the case. I'm sure the fruit they're discussing is relevant to Zunesha, but to be fair we don't even know if they're talking about a fruit ability that is on Wano now.
It's also pretty unlikely that they've been informed by CP0 or other sources about tama's fruit. CP0 only saw the ultimate effect of many headliners switching sides, and that could be caused by a very wide range of reasons in this world of crazy abilities. Kaido's henchment were trying to capture Tama due to her power earlier though, so that little bit of intel coud have been going around for a while and just now reached the elders, but it hardly seems a piece of information that would be considered relevant enough to be shared at such high levels…
All of that is really more linked to the extremely awkward exposition given by the elders rather than the theory in itself, which i insist is really well put together and plausible.
And it's surely thousands times better that it being the gom gom.