Whether Caesar has Monet's heart or not, I'm still fairly confident that she'll end up becoming a female Pell.
Also, back on the subject of Momo's colors being "girly", wasn't there someone here who brought up the possibility of Momo being a girl who was raised as a boy a few threads back? I can actually see that theory being plausible since his human appearance was shown as a silhouette during that flashback of his.
And hey, if that theory proves true and (s)he does join, then that means we'd have a reverse trap as a Straw-Hat! It's a win-win situation!