Nah, the DoA men will not be ever replaced, the only case is Bankotsubo (hoping that will be even the last one). However the female characters are ever been the most popular and they will continue to be so.
Considering the new additions in DoA5 compared to the rest of the series and, at least so far, in DoA5U compared to vanilla, we got 5 male characters and 8 female ones: the women are more as predictable, but the proportion appear to me pretty balanced.
What influence this way to see the things is that 2 male characters are guests and other 2 are old acquaintances making of Rig the only new addition (anyway IMO very cool). On the opposite between the female characters there are 2 guests and 6 characters new entries in the series with mixed originality in appearences and movesets.
But we have however 5 slots that TN decided to dedicate to the male gender: with Ein and Leon already present in DoA5, I'm pretty confident that we would have seen 2 new male characters in their place in 5U (maybe 1 with a TN deciding to bring back Bankotsubo as a disc content).
All this for saying that if TN will keep the current roster of characters and policy behind their addition in DoA6, I think that we will see more than only 1 new DoA male chara in the next game.