How about implementing some similar concepts from Elder Scrolls Online? I know that's an MMO game, but once you reach endgame in ESO, there's really not that much difference. You've completed the story and just focus on adding tiny bits of DPS whilst running dungeons/missions.

The concepts I'm thinking of is research and home. Adapted to The Division 2, it would be something like you getting a flat or house in some way (in-game reward or money purchase). Then you can add furniture and facilities to this. Or buy a new one if you outgrow or get tired of it.

Getting furniture requires you to craft it. So you have to scavenge parts and blueprints.

Believe it or not, but a large amount of people in ESO spend most of their time home decorating. Just playing the odd mission here or there to get parts.

I for sure would like to get a flat. Or a house. Or an underground bunker!? A house boat? A winnabago? Yes please. I'll invite you all for my moving in party.