FFS, I need to hang around here more often again.
I have a confession, I used to rag on KOEI for making so many of the Warriors games. That said, I got ahold of different games finally and have pulled an about face. DW2 is a cheap bastard, but now I see how much better DW4 is all around, and then how 5 is better. Samurai Warriors 1 is OK, but I played Orochi 3 for about 5 hours before I realized the sun was rising. The one irritation I have consistently is that my allied officers are generally as useful as a cardboard cut-out as I always seem to be having to save their asses.
As for a new 'Warriors' spin-off/team-up, many of the suggestions are good to great, but aside from the comic-book setups almost all are based on JRPG, which is not a real issue considering the ROTK-DW direct connections, but I do have some that I think would be a change. They are also out there, and likely wouldn't ever cross the mind of any sane being, but sane I am not.
-Warriors Orochi 4- Orochi attempts to destroy everything again, links Three Kingdoms China and Feudal Japan AGAIN...but also, and here's KOEI's chance to change it up, Orochi has also linked to the modern day, or at least relatively modern day.
-Brutal Warriors- The first half of Brutal Legend had me happily hacking away at enemies, and some of that was likely getting lost and slashing my way around the map, but I digress. I think the entire premise of Brutal Legend could be taken and made into something much bigger that what we've seen. Not everyone is a fan of rock, but who said ALL the characters had to be metal-based. Have another "Pull this random guy from the future" bit, and...I dunno, that's as far as that one got.