Evidence that has an actual basis:

1. The timeline would match up
2. We know from all the way back when Boa Hancock was introduced that she was the Kuja Empress who died of lovesickness, which could be part of it

Evidence that's subjective:

3. She does kind of look the part, right?

Evidence that's a little specious:

4. She was introduced in chapter 1156, and the number 56 has always been associated with Luffy, because of Japanese puns. 5 = go, 6 = mu




Evidence that I'm extremely skeptical of

5. People keep saying that there's a 56 hidden in her hair.

I'm going to be real wiht y'

all

I do not see it

I see the six, it's that little white swirl in her hair

But supposedly the 5 is the shape of the inside of her ear and

That don't look like a 5 to me

I totally see that five in her ear but that's very skeptical

Anyway, here's a called shot: if she is Luffy's mom, the 'lovesickness' that caused her to pine away was actually about being separated from her son.