Remember when some of us thought that Moria would play a role in the Wano arc.
I think Big Mom is basically Moria, but sort of done right.
She has VERY similar powers, a sort of similar build, and is part of the three great powers.
Also, in Thriller Bark, the SHs fought two Warlords back to back and failed to bring the second down.
In WCI, they fought two Emperors back to back, though they failed to bring both down actually, but they at least got some of BM's important goons before leaving.
Plus she later appeared in a war arc with a fellow Emperor, just like Moria appeared in Marineford with his fellow Warlords (though I think he got kicked out by then but I'm not sure).
And they also fell to former Warlords too, Moria was temporarily KOed by Jinbe and Big Mom lost to Kidd and Law, the latter being the former Warlord obviously.
May be a stretch ofc.