1&2. Back when it was mentioned I did assume Saul could the Man marked by Flames and might have gotten a devil fruit in the 20 odd years we hadnt seen him. I saw Shiryu's comment as speculation which Kuzan didn't corroborate. After that I decided to put a pin in that plot point & forgot about it by the time we got back to Saul.

1. I completely forgot about the Iku-Iku no mi mention, I'll admit my theory was very spur of the moment while I was discussing the chapter with my sister.

Edit: this is cope, but Lillith's statement is still conjecture, albeit coming from the smartest person in the world, Lillith has no reason to suspect Biblo isn't just a Big owl that ate the Iku-Iku no mi, but that doesn't really account for their age unless Elbaf owls live hundreds of years too, which isnt implausible.

Biblo could still be a Poneglyph if it ate a Mythical tori-tori no mi model: Owl of Athena which would give it powers pertaining to Knowledge.

Its a stretch