While I agree that we're likely both overestimating and underestimating just how intensive implementing a female protagonist would be, I just remembered that the specific themes of P5 might make things even more complicated. As much as I would dislike things to be so oversimplified and defining, the mere characteristic of being a girl could potentially alter how the main character deals with the themes of the game, in terms of personal issues and trials to be overcome.
I think one of the biggest problems right now is that we know next to nothing about the game, save for the fact that it exists. There are so many ways that Atlus could have prioritized its development budget that we don't know how much of a butterfly effect the slightest changes might have om how much additional money might need to be poured in. It could very well be like SMT4 where 90-95% of the game is voiced, but it could also be significantly less. There could be hand-drawn cutscenes, just as there could be none at all. At this point, they obviously needed to have sat down and decided what they would need to prioritize and what could be excluded while still making a quality game. I just hope that whatever they chose, their individual characterizations and treatment of particular issues aren't handled so deftly.
Oh and Inorigio, did you consider how much of a difference how voice acting is treated between America and Japan could affect things? It definitely seems that very few roles have enough staying power and viability to sustain one's well-being, but also remember that voice actors aren't being the only ones paid here. Between just the basic components like booking recording studios and working with booking agencies, there is still quite a bit of money being passed around (arguably a disproportionate amount going more towards the auxiliary services, but whatever). Plus, even though the presence in popular culture between the two isn't all that drastic, voice acting is considered a much more respectable profession over there, so that alone could alter the perception of how much is put into each individual piece of work. Unless anyone specifically interviews a seiyuu over there, I don't think any of us have any idea how much even the smallest changes in idiosyncrasies could affect how even rudimentary things like basic workflow could alter.