A big change for the franchise, but one gamers have been begging to happen.
In a blog post, the Assassin's Creed team said, "This year, we also are stepping back and re-examining the Assassin’s Creed franchise. As a result, we’ve decided that there will not be a new Assassin’s Creed game in 2016. Since the release of Assassin’s Creed Unity, we’ve learned a lot based on your feedback. We’ve also updated our development processes and recommitted to making Assassin’s Creed a premier open-world franchise. We’re taking this year to evolve the game mechanics and to make sure we’re delivering on the promise of Assassin’s Creed offering unique and memorable gameplay experiences that make history everyone’s playground.”
Ubisoft did lay out it's plans for the next fiscal year (April 1, 2016 through March 31, 2017) and there were a few surprises in the mix. The games included were For Honor, South Park: The Fractured But Whole, Ghost Recon: Wildlands, a new Watch Dogs game, and “a new high-potential AAA brand with strong digital live services.”
So, we will be seeing a new Watch Dogs game instead of an Assassin's Creed entry, and Ubisoft has an announcement coming up for something they think will be big. What that game is, or when we will know about it, is unknown at this time.
(Source: Assassin's Creed team blog)