A fully feasible and complete plan would take more thought and time than I want to spend on this, but I will spitball some ideas in a direction I'd like to see things go.

X.0
> Deep dungeon is available from the start of the expansion
> 'Relic' type grindable weapons and armor too
> Number of normal dungeons is vastly reduced to free resources
> New PvP mode is added, can be used to grind pve gear strength
> Raid format changes each expansion, doesn't need to adhere to 4 boss rooms
> Field zone size and number is also flexible, doesn't need to be 6
> 1 new type of battle content, may replace Trials, may include mounted combat

X.1-5
> 1 new field zone per major patch, MSQ mainly takes place at new location
> X.3 mid expansion adds 1 new type of pve battle content (eg. endless/survival)
> Raids can be individual and unique, not locked into a longer series
> Re-tuned Unreal content each patch, not limited to Trials, to boost patch volume
> PvP content and rewards each X.2 and X.4 patch maybe
> Ultimate raid can continue as is, each X.1 and X.5

Ok so far what I got there is long term grind content arriving earlier, with world building content coming later and steadily through patches.
If I say more I'd have to explain changes to currencies, tokens, equipment, item level. In short I'd like to shake up the way rewards are earned from content and the involvement of crafting classes but that's another discussion.
btw Unreal World of Darkness and other old raids at current level cap, higher difficulty would be a fun way to give players more things to do without spending much dev time.