Substantial things a player can continually work on/towards that don't get reset every expansion like power/levels do
Of the top of my head things like
1. Player housing
2. Racial storylines
3. Building Capital zones & cities
I understand why blizz has to reset gear progression fully every expansion and partly every patch, but they're not doing themselves any favours by leaving it at that - which basically tempts players to sub for a month, update their toons and wiat till next patch to sub.
They need good, attractive long term things players find cool and exciting they can work on throughout their wow lifetime that doesn't get reset. I really thing
1. Race Campaigns
2. Building up your race/capital city and zone over time should be it. (also includes your house)
E.g. 10.0 Starts massive race campaigns - based on the core races (allied races are part of a core race campaign storyline and progression). These quests do the following:
Advance the story of the race
- Build resources towards the current expansions new system
- Build resources that you can invest in your capital city and capital zone [basically blizzard can add wings and buildings to a city each patch that you can unlock. Designers already have art concept for full city and full restored zone, they work on a section of each city for each part, and in time city and zone get built up, restored.
- Empower you and your race each expansion with different things (e.g. NElves: 1st expansion resources also empower Well of eternity, boosts racials and class abilities, next expansion it's Shaladrassil - each race has something.