The idea I had was that players, through guilds, would submit requests to be filled instead of them being given out by NPCs. Based on variables such as the value of the items, difficulty of the quest, time limit, etc. upon completion, the guild gains Quest Points (QP). QP in turn would be either the main or secondary component used to upgrade the guild (allow for more members, buffs, special guild access only areas/content, housing, PvP entry/equipment, etc.) giving reason to do quests while simultaneously helping to establish an economy for people to toss their gold and time into. It would also be a huge benefit to PvE players who want to help contribute to a guild's standing/rank since the barters and crafters would be a huge pillar in the guild while also giving them a reason to exist to serve both players and the guild.
The regular players who do not wish to partake in guilds would still have a numerous amount of quests to undertake for the rewards guilds offer, be it items for money or money for items, but they would not gain QP from doing so. You also couldn't guild hop to earn QP either, only QP earned in a guild can be used for that one (possibly allied ones who've ranked up high enough as well might be viable). This would allow solo players to still benefit from questing, aid the economy in general, but still place a huge emphasis on being in a guild for full benefits.
On the managerial side, it could be set up so that the Treasurer of the guild could be responsible for the acceptance of quests from players as well as the creation of quests from the guild to players (I'll call it for lack of a better term for now the Guild Mission System or GMS). The Guild Master can decide on if they want:
a) Treasurer to have full control over GMS
b) Treasurer needs GM approval for GMS
c) Treasurer needs approval on GMS actions through votes from high position members in guild.
As a player, I wouldn't mind doing quests if they ended up helping me to not only get something I actually need, but also do something beneficial to a guild in the first place instead of just being another body and member of a highly ranked guild.
If they made this a game where every drop had a purpose, this would really work out well. Just a thought though.