It sounds like both the Dead or Alive and the Ninja Gaiden series are on track to receive respective reboots.
We haven't had a new entry in either series for a number of years, but according to a recent report from Ruliweb (thanks, VGC), that soon might change. The report shared that Team Ninja president Fumihiko Yasuda spoke during a panel at the G-Star conference in Busan, where he said he was working to bring fans news as soon as he could.
Interestingly, a slide at the end of the panel showed a pair of images showing Ninja Gaiden and Dead or Alive along with the headline "The future of Team Ninja - Reboot of popular series," in Japanese. Obviously this doesn't outright confirm brand new games are coming right around the corner, though it does very strongly suggest that we can expect something in the future.
Dead or Alive's last entry wasn't that long ago, most recently in 2019 with Dead or Alive 6, though that one had the ridiculous problem of charging up to £74 for just one of its season passes. Which to be clear, contained two characters and some costumes. Yikes doesn't even begin to describe it.
Ninja Gaiden, on the other hand, hasn't had a mainline entry since Ninja Gaiden 3 in 2012. A remastered collection of the three main titles was released last year, but that's about all we've had from the series in about a decade other than one spinoff game.
Earlier this year, Yasuda spoke with VGC about the Ninja Gaiden series, noting that Team Ninja wasn't against the idea of outsourcing development of a new game to another studio.
While Team Ninja hasn't worked on a new Dead or Alive or Ninja Gaiden game in a few years, it doesn't mean the studio hasn't been busy. Wo Long: Fallen Dynasty isn't very far away now, and Rise of the Ronin was announced in September as a PS5 console exclusive.