I would implement the following:
Each season would feature a new famous WoW NPC.
There would be a story and side quests associated with the new companion that unlocked transmog and new abilities as the story progresses.
The delve mini missions should have more effect on the delve mechanics and should be a player choice. Each mini mission could be catered towards a specific type of spec. Healer, tank, ranged dps and melee dps.
The gearing level or stones dropped would increase as the tier increased until hits max but only for solo play. Groups could get rewards similar to the current reward system.
Max difficulty would be tuned to be on par with some of the harder Elden Ring bosses as a solo content befitting mythic level gear.
Make some outdoor delves.