Description of your improvement: This allows everyone in the server to have an opportunity to do dragon hunts. A Dragon Buff (72 hours) gained from clearing a dragon instance blocks characters from farming dragon instances non-stop, and can actually eliminate monopoly in the market. Dragon key could be an adena sink to help with the server economy as well. Removal of daily dragon spawn, so we don't overflow the market with dragon drops. I think the dragon buff is universal, meaning cleaning fafu instance prevents a player from doing antharas instance also. (need verification from others on this)
Why are you suggesting it? (What does it solve for?) I believe this is how it's set up on other servers. This way, other players still have the opportunity to hunt dragons whether or not they are in PvP pledges. It makes dragon hunts more of a guild dungeon thing and mitigates people from griefing.
How it currently exists today: Right now, dragons are being slain mainly by one group of people, which disables other people from being able to hunt dragons. Dragon spawns once a day, and they are slain while people are working during the day. This creates an unfair monopoly for one group of people. Unlike L4, which is timer based, has 3-4 spawn cycles a day, which allows people to have a chance to participate in L4 still.