I think I've stumbled across an idea that would correct a lot of the common complaints about the endgame: Challenge Runs.
As it stands, two of the most common complaints about endgame are that A) Grinding FSC for crowns and rads is what most people end up doing day after day, and B) the meta is very limited, with most people running BK or Chaos sets and little else. We could solve both of these problems by introducing what I'm referring to here as Challenge Runs.
My idea is basically this: for tier 3 arcade runs and danger missions, give a bonus crown reward if you complete that run from start to finish with a randomly selected tier-appropriate set of armor, and maybe a weapon. To incentivize players to do these runs, the reward would have to be big enough to be at least equivalent to (or maybe even more than) doing vana runs for the same amount of time, so there might be some work there to determine how big the reward should be. This would both give players more options for their resource grinds, and incentivize players to build diverse arsenals. Given how long some people have been running FSC, a lot of folks would probably welcome the opportunity to play outside of their comfort zone a bit.
If this were to be implemented, it might be good to lock it behind vanguard rank or some arbitrary prestige threshold, so that the main draw for newer players is still completing story missions and getting to grips with the basics of their arsenal.