I think this is a fair bet, Phil. When it comes to reproductive health, breast cancer in men (and they do occur, but unfortunately horribly stigmatized), breastfeeding right now debated on whether it's a right or a privilege, and the presence of babies and dependents in the workplace. There are certain functional differences when it comes to the reproductive organs themselves that I can foresee being examined more closely and the ethical framework of what is fair. Men overall are not directly imacted by uterine and cervical health in the way women are impacted. Women are not directly impacted by prostate and testicular health in the way men are impacted.
Also consider the awareness campaigns that hopefully will continue to increase benefit and protection for transgendered individuals. I remember even some Third Wave feminists who balk at the notion that a transgendered woman is not considered a "real woman", in spite of her gender identity and feeling trapped in a man's body with male genitalia. I think the introduction of queer rights as an important overlap of feminism with GLTBQIs rights forces feminism to give ample consideration on gender fluidity with the transgendered and intersexed individuals.
I predict in time we will see a portion of transgendered feminist writers who will be part of the pioneers of Fourth Wave. As the introduction of lesbian and bisexual female writers, the riot grrrl movement, globalism, and ecofeminism as distinctive of Third Wave, my first guess is listening to the observations of feminism and what it means through the lens of the transgendered. Perhaps continuing to break down stereotypical and oppressive gender roles can we continue progressing forward toward equality....or as you mentioned....fairness.
I view the alignment of GBLTQ rights and feminism as being a fairly definable difference between third and second wave. Much of the dislike of trans people by feminists seems to be contained within the second wave, with third wave being more comfortable with the idea.
There already do exist some transfeminist writers. I read some of the blogs at Freethought Blogs, a large multi-author site that tends to focus on the intersection of atheism/skepticism and feminism (I've gotta love that combination, right?), including dealing with sexism within atheist movements/organizations, among other types of intersections like the Black Skeptics blog on the site. At least two of the blogs there are by trans women, with one of them in particular writing a lot about the intersection of feminism and trans issues.
I think one of the most valuable perspectives that trans people can add to feminism is the fact that, if they transitioned from one role to another, they experienced life in the role of both sexes. Usually, women experience society only as women, and men experience society only as men, but trans people are like their own "control groups", where the
same person can discuss how they
personally were treated differently as they presented their self as one sex or the other.
For example, I've seen trans women describe how when they were presenting as male, women were more likely to view them as a subtle threat, and were much more open after the transition when the trans woman was presenting as female. Or how being male allowed them to easily be heard in conversations, but after transitioning to female, men as a general rule in a group conversation tend to view their opinion as less valuable in a conversation, or cut them off while speaking more, even though nothing about the person's knowledge or qualifications changed. Those are some unique perspectives, that basically include a control group of their own self, that only trans people can describe.
Trans children are also an interesting topic. Some old-school therapists are still basically in favor of reparative therapy; that a male child should be given traditionally male toys and instructed to play with boys, and vice versa, in order to try to avoid the outcome of transsexualism, while other thereapists are of course in favor of allowing the child to express herself or himself as the child wants, and letting the chips fall where they may. It's also observed that parents are more likely to bring gender non-conforming boys to therapy than gender non-conforming girls, because tomboyish behavior in girls is often viewed as acceptable, or even desirable, while feminine behavior in boys is often viewed as a downgrade, or grossly inappropriate. That in and of itself says something about how society views the value of stereotypical masculinity and femininity.