USB Host Mode?
Yes, ICS supports USB Host Mode. The Galaxy Nexus definitely supports it with its hardware, too, because it was announced that it would support USB game controllers. How it will treat attached flash storage is not known yet but it is almost certain that the functionality will be there. Paul, the founder of Modaco has published a modification of the kernel that provides compatibility USB Host

I hope that extended battery does still included the Near Field Communication module. Otherwise you lose NFC capability like Android Beam.