Yves Guillemot confirmed that Ubi has unannounced Vita titles coming this year. Doubt we'll see another AC with Sofia on Black Flag, though.
Correct.
Black Flag began development in summer 2011, Ubisoft told Eurogamer, while the company was still busy applying the finishing touches to Assassin's Creed: Revelations.
Since then, Ubisoft Montreal, Singapore, Sofia, Annecy, Kiev, Quebec, Bucharest and Montpellier have been working on the project, while others were kept busy with last year's Assassin's Creed 3.
http://www.eurogamer.net/articles/2013-03-04-eight-studios-working-on-assassins-creed-4-black-flag