Despite the raids being one of the major pulls for players to constantly return to Destiny, Bungie has revealed today that the House of Wolves expansion will not feature a new raid.

Instead, the company will offer a 3-player battle arena mode called "Prison of Elders." That's right, Bungie is not going to offer one of their strongest game features (raids) and is replacing it instead with something that either sounds like another PvP mode or, dare I say it, a horde based mode. Yup. Good call on that one!
House of Wolves will not have a Raid activity. We didn't make this decision lightly. Our team has been humbled by the reception of Raids in Destiny and we are creating a new Raid for a release later this year. House of Wolves will have a new cooperative end game activity focused on variety, replayability, and skill – a new battle Arena called The Prison of Elders.

Bungie plans on releasing new information on every Wednesday leading up to the House of Wolves release. On the 22nd, they'll talk about The Reef. On the 29th will be the Trials of Osiris (PvP) and May 6th will be about the Prison of Elders.