To be honest, I think Oda is playing at something here. Back during WCI, I made a theory that part of Mother Caramel's soul is still lingering within Big Mom, and that's why we see her go through these drastic mood swings. Whatever people might say about the amnesia plotline, I think it served a much bigger purpose than to just get her to help the Straw Hats for a little bit.
When she got amnesia, we actually saw the same Big Mom from when she was a child. Yeah she was still self centered and could get angry, but the key difference is, there was no malice or bloodlust behind her anger. It was so tame in fact that Queen actually stood up to her, and fought her. But when she got her memories back, all it took was a single glare from Big Mom, and he was pissing his pants.
So far we've see three versions of Big Mom.
1) Hunger Pangs - Always Bloodlusted
2) Amnesia - Happy go lucky, without a care in the World
3) Base - A mixture between the two.
With that being said, I think Big Mom's next "change in personality" is one where she completely reverts back to the Big Mom from her youth, which is the one we saw when she had amnesia, but in this regard she'll still keep her memories. Oda has placed way to much emphasis on Big Mom's emotional state throughout the last two arcs for him not to bring it to some sort of conclusion.
By the way, I was just thinking about making a thread on this subject the other day, and then completely forgot. Funny how it worked out that you made one, and it reminded me.