Allow quest makers to reward "reputation with their guild" for completion of a quest. But it does raise some concerns:

• Would need to extend the Blizzard reputation frame to include custom reputations. No idea what the LOE would be for this.
• Who would be allowed to create quests for a guild's reputation? If anyone can make a quest to reward themselves 36,000 rep with any guild, then the reward would be pretty pointless. This sort of management might be better suited for a standalone addon that integrates with PMQ.