Unlike the Darkmoon Rabbit, Moonfang will apparently be "summonable"... sort of. By killing enough wolves on the island, Moonfang will spawn, at least according to this Wowhead comment.
Additionally, a poster on the WoW forums noted that Moonfang will be similar to the Timeless Isle rares (similar 1 hour-ish timer and all), and anyone and everyone will be able to tag it/have a chance at loot. If this is indeed true, this will be a huge step up from the Darkmoon Rabbit which required you to be in the raid that tagged the boss. It will remove much of the griefing (but not all, of course) and give everyone a fair chance at the vanity items that drop from Moonfang. This style of loot distribution for a world boss definitely gets my two thumbs up.
The main question now is will players only have one chance at loot per day? Or can players kill Moonfang as many times as they please in hopes for a drop (same as Timeless Isle rares)? If the former is true, then we'll need to start parking all of our alts on the island for a chance on each one. Unless... it's an account-wide chance (bleh). But we'll see what the mechanics are for loot once players start killing this new DMF boss.
My hope is that it will be similar to the Timeless Isle rares, and players will only need to invest some time and effort into spawning Moonfang and killing it.
If things are balanced enough, a "low" droprate paired with the ability to attempt countless of times per day will be a fair situation. If the droprate is "high", then having a "once per day" mechanic would be understandable. Another thing to consider is that this event is only around one week out of the month, making the time limitation another factor that needs to be added into the equation. It's all about balancing the RNG with everything else to ensure that it's not too "easy" yet still fun.
Last but not least, I'm curious as to how Moonfang's stats will scale depending on the number of players attacking it. The rares on the Timeless Isle increase in health as more players tag it, but it's entirely possible for a single player to take on one of those rares by him/herself. I doubt that Blizzard wants players to be able to solo the new DMF world boss, though, so I'm wondering if Moonfang will have a set health pool and hit like a monster truck even without numerous people attacking it.
If that's the case, then a large number of people will definitely be necessary, meaning that summoning and defeating this world boss will depend heavily on participation on the Darkmoon Island. That could spell trouble for lower population realms, and/or once the novelty of the event has died down.
We'll have to wait and see what's true and what's not at the start of next week. Things could have changed between the PTR and patch 5.4 release, so it's all still kind of up in the air. I'm crossing my fingers in hopes for a good scenario for collectors, though.