{quote:jpmsi}
(...) imagine that you instead register with the web application a remote location, where you can get a certain plugin. You could then use a special class loader to load the remote plugin and incorporate it into runtime. Wouldn't that be great? You could even do some pretty neat stuff, such as dependency checking, remote dependency resolution… Even obtaining a plugin directly from CVS/SVN and compile it into runtime!
{quote}

Well technically you can do this, unless you'll need to merge code which won't happen if it's a "production server". 

The low priority thread would just check for updates and synchronize the code. The class loader would detect changes on the local source files, compile them on the fly and load the new class versions.\\
Probably it would work fine on REST web applicatios although if there's the need to keep state you probably will have problems preserving the object states when loading the new versions. Also interface modifications still wouldn't be allowed, but it would definatly allow for example bug fix on at runtime. 

We could write such container, isn't it? :-)