Well, imagine, you had a currency system, and could get reputation as well from all those activities. You would do pvp battles for a faction, do quests for them, or run dungeons or raids. While you do any of those activities, you gain an amount of currency, which you can use to buy equipment you need to progress or vanity items.
You also had faction vendors, who would sell faction specific items. Based on that, you chould simply chose whatever activity you would like to get your character geared. And whatever you play, it helps in character progression.
Well, replayability also is based on how many pathes you have available. If those quests become dull, just go and play some pvp. If pvp becomes dull, play dungeons. This offers way more diversity than the reward being locked to one single activity. Yet, you still work on the character progression your planned from start. No matter if you change your playstyle rapidly.