Recent skaters who've been successful with 3As in the past few years have been young and for the most part, skinny (Meissner, Nelidina, Nakano, Asada). Nelidina has retired from figure skating and Nakano hasn't progressed and to my knowledge hasn't successfully landed a 3A in quite a while. Meissner and Asada are both very small and very slim--and quite young, which is to say undeveloped.
I doubt very much that Liang or Hughes will be adding a 3A to their jump repertoire. They are both stockily built ladies and though powerful, in both cases they carry the greatest part of their weight from the waist down because they are both well past pre-pubescence--BeBe will be 17 in March, and Emily is almost 16. Trying to do a 3A now would be extremely difficult for both. BeBe has had back problems and I don't think she's going to tempt fate by practicing a jump that can make her problems worse.
Katy seems to be going through an awkward stage right now. She is not as tiny and undeveloped as she was last year, and she is probably going to struggle with her jumps for awhile. I think she will eventually regain her form, but I think she's past the stage where a 3A would come easily to her, too. Danielle Kahle was toying with 3/3s and 3As last season, but the puberty monster has ambushed her, too. I'd just like to see these girls get their jumps back and refine their moves instead of going for the big score with exotic jumps that become increasingly difficult to do as they mature.