Dynasty Warriors 10 was in development but canceled for DW Origins
https://www.siliconera.com/koei-tecmo-canceled-a-new-dynasty-warriors-game-before-origins/
In the interview here, they revealed that they had started to work on a Dynasty Warriors 10 that was an extension of DW7&8 gameplay.
I know many will lament this news, but i think they made the right choice. A numbered game with the DWO formula could easily be the best game in the series if they do it correctly.