Good thread, lets analyze with pure logic (although I don't know how much Oda values that these days).
What do we know about the fruit the way the Gorosei talked about it?
1) It hasn't awakened in decades and it was a mystery even for the WG. That means we also probably were introduced to it recently, since the Gorosei only learned and talk about it now.
2) It probably has a curious name, since they specifically say that the WG gave that fruit a "unique name" to hide its "true name".
What DFs currently in contention don't seem likely at all?
1) Luffy's fruit. It just wouldn't make sense that the Gorosei talk about it now, when the entire world saw that Luffy has that fruit's powers 2+ years ago. Everyone has known about it since.
2) Kaido's fruit. Same thing with Kaido. We know that he has been captured by the WG 7 times already and he's also a very prominent player in the New World. He even invited CP-0 to his banquet. No way the WG didn't know about his fruit and just learned about it now.
3) BM's fruit. The WG knew that Carmel held that fruit before BM, so no way they thought it hasn't appeared in decades. Not to mention that BM as holder is too prominent a foe of the WG for them to not know her powers.
4) Law's, Kidd's and Yamato's fruits. More of the same. None of those fruits seem specific enough. On top of that Kidd's and Law's fruits have already been known by the WG for 2+ years (Sabaody incident, Rocky port incident etc.). In Yamato's case it wouldn't make sense either, since either the WG already knew about her fruit (her being Kaido's daughter after all) or if they didn't know they simply didn't see her rn (only government officials in Onigashima right now are busy dealing with other foes).
What DFs are still in contention?
1) Tama's fruit. She tamed almost all the SMILE users, she has been a prominent character without that much in-depth story so far and her fruit really has some creepy master-slave-feeling towards it. Its name "Kibi-Kibi-No-Mi" also has an innocent/cute feeling towards it. Maybe its real name was "Slave-Slave-No-Mi" or something like that?
2) Zunisha. The wildcard. The panelling suggest that there is some connection, so maybe Zunisha is some dude that ate a mythical DF? On the other hand the SBS answer Oda gave makes that very unlikely. He already confirmed that Zunisha is a Naitamie-Norida-Elephant. He even described that species and gave explanations about their life-span and body etc.
3) Orochi's fruit. Well, his hydra powers are creepy and interesting. However, it just doesn't seem like some kind of particularly weird or dangerous fruit and it also doesn't have a curious name.
4) Toki's fruit. Maybe it's just talked about now bc they learned that the Oden's samurai were indeed sent forward in time and arrived in the present. That could mean they now know that the holder of the Time-Time-Fruit resides/resided in Wano. It would also make sense why they say that this fruit was a legend to them and hasn't been seen/awakened in centuries: Toki always jumped a few centuries forward in time! It would also explain their panic, since the user (if still alive) would probably know all the details about the void century. Only thing that doesn't fit is the supposedly curious name of the fruit.
Conclusion: From a pure logic standpoint it has to be a fruit that has been locked in Wano for centuries. The WG knows all the stuff that happens on the outside and all the other DFs from prominent characters (Luffy, Kaido, BM, Law etc.) have been long known to them.
My bet is on Tama's or Toki's fruit or a completely new one as of right now. Those are the only three scenarios that currently make sense.