This is pretty much my guess as well… though given that Brad's VA recently died, they might omit him from the launch roster unless they recorded all his new lines already. I'd assume getting a new VA and re-recording everything is more costly and he's not that popular, or relevant. Also if they safe his moveset, they can slap it on a chick as DLC (Tengu says hi!)
Makes the roster pretty female-heavy, but not much they can do… they simply do not have enough dudes lol
I think expecting 24-26 chars at launch is realistic… they can't afford to have less than DoA5 and they'll get massive flak for any female they omit/sell as DLC… so the NG girls are the safest cuts. I think Phase will be gone permanently, if they need her for the story, they can just make a Kasumi costume where they change the teleport effect and intro/outro.
Phase 4 is probably the easiest character for them to implement so I don't see her being removed. They already have her model from Kasumi and they can just grab her animations from DOA5. And they can re-use Kasumi's breaker blow and fatal rush combo. Plus she was mentioned so much during the DOA5 story and she was shown at the end of the game.
If they do have a season pass, they would need to add popular characters. I don't really see Leon and Ein selling as well although Ein seems to be a bit more popular than other characters judging by character points in the DOA5 (PS4) online rankings. It's not the most accurate way to judge popularity but based on it, the characters in order with the least to most numbers are Akira, Bass, Leon, Gen Fu, Baymen, Raidou, Jacky, Pai, Mai, Eliot, Sarah, Brad Wong, Ein, Zack, Rachel, Lisa, Naotora, Lei-Fang, Nyotengu, Helena, Alpha 152, Kokoro, Rig, Mila, Jan Lee, Tina, Phase 4, Momiji, Christie, Hayate, Honoka, Marie Rose, Hitomi, Hayabusa, Ayane then Kasumi.
Ideally, I believe DOA6 should at least have everyone that was in DOA5 vanilla plus the two new characters and Phase 4 as the boss. I'd like to see Rachel in the roster as well because she fits the more serious theme of the game compared to most of the females. I could see them replacing some old fighters with newer fighters. Make a new male with Ein's old moves along with some new moves then they could sell him as a new fighter in a DLC pack. I think if had a similar look then he could appease the old fans of Ein. Although Ein does seem a bit more popular than I thought so I would probably change a less popular fighter. Bass seems like he was based off of Hulk Hogan who was popular at the time but maybe making a new character similar to The Rock or John Cena with Bass' moves might be more popular. Leon still seems too similar to Baymen to me. Their fighting styles have been becoming more different since DOA2, but their personality, look and size is similar. I think they should change Leon a little bit. Maybe a DOATEC experiment that made him into something like the Hulk or how Marduk might be Gigas in Tekken 7. This is the only way I could see paying for old characters as DLC. They would have to be re-worked into new characters.
Unless they are planning on making some bigger changes to gameplay or to characters, I don't see why can't add in most of the DOA characters. DOA5 is on the current gen consoles. Casual fighting game fans will probably notice that DOA6 looks better but if it's not too different, they might just stick with DOA5 or not notice it. Plus there are so many fighting games out there now. So DOA6 can't use the bad press.