It has been confirmed by Muts that Backtrack4 will be a full distro and based on Ubuntu and the beta for the distribution will be out soon.
http://backtrack4.blogspot.com/

This will make the life of many penetration testers and consultants much easier, specially for keeping their machines up to date, specially since for many attacks and techniques one has to "Hack Naked" with out a firewall. I'm really looking forward to the beta so I can start updating my scripts for the new distribution.