I see four sources of pressure that push toward the ordination (call it what you want) of Orthodox women:
- Feminism within Orthodoxy - the desire of Orthodox women to gain titular recognition of their achievements and positions. This is part of the general trend toward egalitarianism and feminism (two separate movements, of which I';m more comfortable with the latter than with the former, ve-acamo"l) within the Orthodox world. This pressure, on its own, is generally counterproductive in that it generally provokes disproportionate reaction. It's necessary, though, in order to drive the movement once other pressures are created. Note, for example, that the institutions of to'enet din and yo'etzet halakha were both born of necessity (the former from the misogynist structure of Israeli divorce courts, the latter from the recognition that women are far better purveyors of hilkhot niddah than men are).
- Other Jewish movements - this is not to say that other denominations put pressure on Orthodoxy to do anything. That would, again, only provoke reaction. However, the fact that there ARE non-Orthodox women serving as rabbis in non- or quasi-rabbinic positions (Hillel directors, federations, funds/ endowments, think tanks, community learning programs, NPOs, etc.) puts pressure on the Orthodox community. Many Orthodox women who are equally or better qualified than non-Orthodox applicants to the same position are at a disadvantage due to their lack of recognized credentials. This flaw is not fatal, but it is definitely an obstacle.
- The changing role of the "Rabbi" - the historical role of the 'rabbi' is the subject of many books and dissertations. There is no doubt however, that it has changed yet again in the US in recent generations. Any religious functionary is now a 'rabbi' - from the first-grade rebbi to the kashrus supervisor to the 'kiruv professional'. Some would argue that the title has been rendered meaningless. I would not go that far; rather, it has a connotation of being a provider to Jewish religious services. Semikhah itself has followed suit. One may get semikhah online with shemayisrael.org. Ner Israel offers a semikhah for mastering 5 volumes of the Mishnah Berurah; I've even heard of a semikhah in Israel (for 'kiruv professionals') which involves a test on 50 blatt Gemara of your choice as well as mastery of the Kitzur Shulchan Arukh. It's hard to know why exactly this change took place, but here are some possibilities: a) the desire to generate more respect for these otherwise minor functionaries (it would be interesting to look at Torah U-mesorah archives to see if they ever made a decision to have the rebbeim addressed as 'rabbis'); b) the general compartmentalization of Jewish proficiencies due to advances in technology and communications: a rabbi used to have to know all about paskenin maros as well as treyfos. With the advent of refrigeration and overnight mail, he needs to know neither in order to be effective. Thus, instead of a single, general role, you have numerous smaller ones, all of which are called 'rabbi'. It could be that smaller roles existed in earlier times, but were not called rabbi> Rather, it was melamed, magid, shochet, mohel, etc. Those divisions may still exist, but all are still titularly 'rabbis' (Rabbi Ploni Almoni, Certified Mohel) - kind of like 'doctors'. Thus, the term has become a marker that says 'this person is an authority/ service provider in the following area'. As this perception grows, there would be an increasing need to do the same for female 'service providers'. In several senses, this has already happened - both with new titles like 'yo'etzet' and 'to'enet' (which, I believe, will ultimately be subsumed under 'rabbi' like 'mohel' and 'shochet' were), and older ones like 'rebbetzin' and 'rabbanit'. Nevertheless, none of these terms offer the blanket coverage that 'rabbi' does. Only the wort ostriches still believe that women do not fill roles that are currently being filled by 'rabbis', or that they lack the requisite knowledge that it takes to be a rabbi. It's about title, nothing more.
- Money - there's money to be made and money to be saved by women who have some type of clerical title. Perhaps the financial pressure is not yet so great, but it's there, and it will grow. As we all know, economics are a much greater stimulus of halakhic innovation than ideology or anything else.