Reddit slouth, KevinDavid40, has now uncovered two sets of information relating to The Division 2's raid. Set on Arlington Island, and accessed from Arlington Memorial Bridge, it looks as though there's plenty of rewards, commendations, trophies and missions. There's also a couple of outfits available, with Legendary and Exotic versions up for grabs. 

In a new post, he details further information on the Raid including its 8 core mechanics (here's one of them below).

Location Objective Mechanism - Arlington Bridge - Surviving the Assault:

8 players will attempt crossing the bridge on a giving time. One agent will be randomly marked to NPCs, and will be able to spot the hidden escape route, all remaining agents will do their best to cover his back all out to safety. 

If you want to view the rest of the mechanics, jump here.