The base idea behind all of this is to have "jrebel for osgi". Which means you can life edit a class and the containing bundle should be automatically redeployed to the OSGi engine.
Karaf (and it's related projects) provide interesting features like "dev:watch" and exploded bundles which could in theory allow automatic redeployment of bundles you're editing in; the moment you save a class in eclipse.
There are various possibilities how this could be implemented. The most interesting solution is one which works (a) fast and (b) could be integrated into every IDE.