From the blog panel:
-Co-op characters will switch out between Cole, Carmine, Anya, and ?
-Berzerkers and Brumaks will be in Horde 2.0.
-There will be cosmetic customization. That pertains to either weapons, armor, or both.
-33% of the time you'll be fighting the lambent locusts, as opposed to the normal ones.
-You can unlock everything (items for multiplayer and campaign) just by playing the campaign.