Tecmo Koei has posted a banner on their Expo page which states that Samurai Warriors 4 will indeed be releasing this Fall for the PlayStation 3, PlayStation 4 and Vita. They will be showing the game off in a debut trailer at the MCM London Comic Con for the first time, and I'm assuming they also plan to show the game off at E3 which is only a few weeks away.
Given the popularity of the Warriors series, it's safe to assume that even though the game is being debuted in London, that it will indeed make it stateside.
It's worth noting that the game isn't listed for any of Microsoft's consoles. Dynasty Warriors 8 was the last main entry title that appeared on the Xbox 360, but Xtreme Legends only came out on Sony consoles, and it seems like Tecmo is continuing this trend for Samurai Warriors as well.
The banner does state that the game will be unplayable at the London Comic Con but here's to hoping that there will be a playable build at E3. If that's the case, you can expect some hands-on, or at the very least impressions of the latest hack 'n slasher.