Tecmo Koei has revealed that Samurai Warriors 4 is in the works, but there's going to be quite a wait. The next Nobunaga-flavored hack n' slash sequel is set to coincide with the series' tenth anniversary ... in the year 2014.
The first Samurai Warriors launched in February 2004. February 2014 isn't yet confirmed as SW4's release window, but it's the one that Tecmo Koei's aiming for.
Of course, we're talking about a Warriors game, so the wait for SW4 won't be bereft of spin-offs and sequels. Samurai Warriors: Chronicles 2nd for 3DS is scheduled in September, and there'll doubtless be way more titles in between.