I’ve updated the Grails roadmap with what we plan to work on through the course of 2012. Initial work is around refactoring our build system so that it can easily be reused by the Maven plugin (which will help us get setup for the eventual migration to Gradle).
Then there are some key areas targeted for improvement including our handling of encoding / escaping in views to improve security and a long overdue rewrite of the data binding infrastructure including a flexible API to allow additional data binders.
The much asked for ability to namespace controllers, domain classes and views is scheduled for Grails 2.2.
Towards the end of the year we plan on working significantly improving the development of REST based services in Grails, which ties nicely into the aforementioned data binding improvements as data binding applies not just to form data but to JSON/XML data too.
Let us know if there is anything you would really like to see improved / added to Grails, but remember that many things can be added to Grails via plugins, so features under consideration apply only to the core platform.