Croco-mom interests me, because it would make Luffy's interactions with Crocodile INCREDIBLY fascinating, and explains Croc's behavior during Marineford. I also like the idea that Croc is Kuja, who is Tritoma's sister, and hates Dragon for "killing" her sister via Love Sickness.
Imu pretending to be Eris interests me, but, the "Teach being the son of the literal Devil" kind of throws me off.
I liked the Eris = Imu theory at first, but I think it has too many holes the further you go into it.
Imu having KILLED Eris, and taking her place, to Domi Reversi Rocks, would be very interesting.
I still doubt this, tho, simply because Teach has been portrayed as being close to his Mom, and Oda's been showing us through God Valley that babies are good judges of character, with Shamrock crying the moment Maffey picked him up.