I know we've already had this conversation a thousand times, but the resources argument probably is a significant factor more than just fan reception, especially when you consider how many assets the female cast share. For DOAX, the work required to add two guys with one or two outfits could be equal to adapting several members of the female cast; with in-built compatibility with a plethora of easily monetised swimsuits. The better decision from a financial perspective is clear.
The couple of costumes the men have gotten in the main series does show they're not completely averse to focusing on them when it's feasible to do so (leaving aside the actual quality of the outfits, in certain cases), but a lot will have to change with the next main game for them to be confident that greenlighting a DOAX4 expansion with males would be adequately profitable.
There are financial aspects to be taken into account for sure, but with the nine ladies they already have in the game, even if they didn't add anymore female characters via DLC, I think they have more than enough built-in assets to leverage at a premium. (Which is something they already do quite handily in DoA5. I'm not saying I approve of this structure as is, but it certainly must do well for them if they're still supporting it three years after the initial release.)
Will they have to divert some resources away to work on a few guys? Of course, but in the end I think it would be worth it. Sticking exclusively to their wheelhouse of cheesecake is a safe choice in the short term, but not in the long run. As I've mentioned before, if Team Ninja doesn't get the jump on this type of content, another developer will, and they'll be left holding the bag. I don't think every game has to be suitable for all audiences obviously, but the potential to expand into the realm of beefcake is already there with DoA, as they have a strong stable of male characters that are sorely underused. Start with two guys, enough to have a team for volleyball. (Ideally I'd like four, but even I know that's a lot to expect right now.) The "safest" choices would be Hayate/Ein, Bayman, Ryu and Eliot. (You could make a case for Jann Lee too. Maybe even have him included when they add Lei Fang in.) Give 'em a few sexy swimsuits, which I know would be easier to conceptualize compared to the outlandish bikinis they're showing off, record a few grunts and suggestive lines, and let the players finally have some options. I think the added positive mind share they would gain from this would be enough to offset any initial trepidation. It would probably make it a lot easier to float the idea of an international release out there, and even if it still stayed a Japan only release, it would still find support IMO. Male oriented fanservice is on the rise everywhere.
Really, it's time for them to take a leap and go for it. The sooner they jump on board, the better for all involved.
We've discussed this before. Do you buy a male/gay porn magazine to see photos of naked women? Would you be annoyed if your favorite male/gay porn magazine suddenly added photos of naked women, while either jacking the price up or cutting the existing content by half to cover the additional cost?
DoA is not a female only series though, so that analogy doesn't work. The men are there, so it makes sense to utilize them. I'll say again, this would be in addition to the female related content, not in its stead. I've played plenty of games with female fanservice and didn't feel the need to burn it in effigy for affronting my senses, instead of seeking out the aspects of the game I do enjoy.
There are fans of the male characters, and we deserve to have some content made for us as well.