I have been developing a Seam application in IJ 6 for almost a year now. It has worked simply. The only real extra support that could be added would be for SeamGen. All the other parts are really already handled by IJ, such as
JSF, EJB3, and any AS.
Also, if there was any extra to be built, it would most likely be a third party Plugin, which anyone can build. Unfortunately,
JBoss is mostly concerned with creating their "JBoss IDE" which are plugins for Eclipse.
Mark