The implications is that there are 7 seraphim one for each of warlord, they all have animals names, ( S-Shark Bear Hawk Snake )
So we probably will see S Gecko Bird and Alligator.
I don't think there will be more seraphim.
Does it make sense? No.
A Seraphim of WB, Kaido and Roger would make more sense? Yes.
But Oda has to draw the line somewhere, if we started see Seraphim's of legends/dead people like the Edo Tensei I would've dropped the manga.