Bungie has revealed that the Destiny beta on Xbox will not be running at 1080p. The developer continues to work toward having the game at 1080p on the Xbox One in time for the actual launch.
Because this is a beta, it just so happens that this is where things are at this point in the development. The developer is striving for 1080p on all release platforms. Still what is not clear, is what resolution the Destiny beta will be running at on the Xbox One. So far Bungie has not said.
It is likely at this point that we will have to wait till the beta arrives on the Xbox One before we know what resolution the beta is running at on the Xbox One. It could be that this could remain in flux up until the actual release of the beta on the Xbox One sources tell us.