I think it would be really cool to have some sort of DOATEC spinoff game along the lines of a NG.
Antagonists (which are actually who you play as b/c let's face it...things need shaken up once in a while)
Kokoro: Wants to learn more about Helena and after speaking with a manipulative Christie decides to join forces with DOATEC to stop the "evil ninjas" and help her sister (none of the main "good guys" gets killed of course...but Hayate, Ayane, Ryu, and Kasumi could be potential bosses). Could play similar to her DOA version while also utilizing weapons such as a samurai sword.
Rig: Not too sure about him yet since I don't know the full story but he is Donovan's son so of course he's on DOATEC's side. Also fights like DOA self but I can see him as the type who pulls an iron pipe off the wall and beats your ass with it. He seems like the kind of guy who sees the "error of his ways" and turns to the good side in the end also.
Christie: Donovan's right hand man so of course she's in it. Plenty of cool assassin weapons for her.
Bayman: Posing undercover in order to learn more about DOATEC. Not sure what kind of weapons he would have.
Lisa: I can see her having some really neat gadgets as well (she is a scientist after all)
<Insert New Character>: ideally a guy to make it even in the game. Also he would be playable in DOA 6 so he'd need a completely new fighting style.
Helena: Not playable but present throughout the story and obviously important in the end when Kokoro finds the truth (as well as Helena who doesn't want the old DOATEC)
Final Boss: Donovan: Needs to happen