Like many great ideas in Liferay, EXT Plugins came from our community. This idea is credited to the company IBA CZ.
Rather than have a monolithic structure (EXT environment) that modifies the entire portal, we can now modify all of Liferay's core classes using EXT Plugins. Unlike the EXT Environment, EXT Plugins don't require the entire portal code (portal-impl.jar, portal-web.war, etc.) and have a smaller footprint since they only contain the differences / deltas.
This makes it much easier to extend and maintain changes to Liferay core and is more powerful since we can modify util-java and util-taglib which wasn't possible before.
This move is huge and drive us towards our goal of having a light weight core with modularized components that will be easy to develop, maintain and plug into other instances of Liferay.
More information is available at the following links: