EPP is the productized version, this is the ready for prime-time version.
The current version is Enterprise Portal Platform 4.3 which embeds EAP 4.3
Next EPP will be running on EAP 5, it will depend on your delivery date. You should contact our sales team.
Will JBoss Portal be released for AS 5.x?
No, all development efforts are going in the GateIn project and the EPP5 product, no new feature should be expected in JBoss Portal.
I've been looking at the GateIn portal and while it looks promising it doesn't seem quite ready for prime time. We (I work with the original poster) are considering it as an alternative to the JBoss portal but there are some shortcomings. For example, I haven't come across any way to add new portlets. We will also need to add new skins, and create our own authentication module. Are these kinds of customizations doable, or planned?
I've also played around a little with the GateIn portlet container, but without documentation it's difficult to assess. Will developer documentation be available any time soon? (Or does it already exist somewhere?)
GateIn Portlet Container is a rebranded project of JBoss Portlet Container, the documentation of the previous container still apply:
For the portlet container, the JSR-286 specification document is also a must-read