This would be a nightmare. Distributed processing is "easy" when you can break the workload into self-contained stateless chunks of information. By its nature an MMO is extremely state-ful which makes a peer to peer structure difficult. Then you introduce trust issues (how does my node trust the inputs your node is giving me, how does your node trust the health state information mine sent you, how does OPs ever know what we know). I'm not going to sit here and say it's impossible, that's a sure-fire way to find a foot in my mouth, but there are some major hurdles that are nigh-on insurmountable and dicate that you need a central server of some sort.
Though honestly there is a possibility they could scale back the service and allow people to rent servers but then they need to hire a maintenance crew that could be better serving NCSoft's bottom line by assisting in GW2 upkeep. I doubt they'll ever actually release server code or even server binaries as there's probably a ton of proprietary code that is heavily reused in currently active mmos.