I feel like all they might really need to do to make sure people can still do Eureka post SB is just to remove the sync on the zones. Eureka has kept us synced at what, ilvl 300 the whole time to emphasize the elemental level system, but what happens if you let in level 80 players with ivl 500 gear? Or wherever gear ends up at at 5.0 endgame. Sprinkle in some nerfs to make NMs easier to spawn or a blanket nerf to all the enemies and grinding out Eureka in the future shouldn't be too bad.