We've just received news that the next Halo game will be coming in the Fall of 2015, around the same time as the frachise's first television series.
Bonnie Ross, General Manager of 343 Studios, had this to say about Halo 5:
“Halo 5: Guardians” is a bigger effort than “Halo 4.” That applies to the content and scope of the game, as well as the technology in what’s now a brand new and more powerful engine. Certainly there are some core elements carried over from prior games, but we’ve invested a huge effort in retooling our tech to take full advantage of the Xbox One’s hardware and ecosystem to create worlds and experiences worthy of next-gen.
More information on Halo 5: Guardians will be coming during Microsoft's E3 conference on June 9th, so stay tuned!