Well what DreadEnd is doing has been done on a per world style, but not per player/ individual area. Once you split the main thread you can spread them around different cores such as tickthreading which splits each world into its own which is not as good as what DreadEnd is doing, but tickthreading is public and working while dreadend's terracore is not.
Another part about tickthreading is that it can slow down the tps calculations of a chunk/area so that instead of that area being run 20 times a second it skips it every few, and along with that for a long time there has been async events with bukkit which are as they say asynchronous to the main thread which means that for how fast or slow they go they won't effect your main thread (as long as you don't max all your cores). If you ever used logblock you see a perfect example of a database querry being an async task as you can ask it to find every-single block change in the past week and you won't notice the server lag, but you will notice you won't get a reply to your command for a few seconds.
Personaly I like the comments about refractoring to C++, if someone ever does do it they will have made a beast of a client/server. Right up until we get an update like 1.5 which changed a ton and you nearly have to start from scratch.
