Better rewards... say, minions or furniture, glamour or crafting mats of some kind. Possibly some that are zone based, so any fate in the zone has a chance to drop them.

Expand the bicolor gemstone system to old zones.

Make it so twist of fate isn't lost on zone change (unless that already changed and I missed it, I remember that being the case tho)

More styles of fate... proper tower defense style gauntlet with turrets or something maybe take advantage of the new mechanics they've added, maybe even some that don't require combat at all - like those zoom and scout ones. Dart throwing at targets or something idk. Not a lot of that probably but could spice things up a little.

More chain fates.

Somebody said it already but rescaling some of the boss fates, or improving rewards so people have more reason to bash their heads against a fate that takes 20 minutes to kill alone if it's even possible to do (haven't tried in ages but I'm thinking of the big armored turtle in the Dravanian Forelands).