Why would you want to use the new IOS versions as bases? There are no improvements, only security bugfixes. The old IOS version can still be downloaded with NUSD and other tools, so why bother? That said, I think it is possible. The changes they made to the IOS must be very minor, since the version number was only incremented by one (other IOS updates had much more significant version number differences and still no improvements, only bugfixes)
EDIT: Just read megazig's post. Seems the WLAN module of IOS has also been updated, which is unusual. But it's yet to be determined if there's really any improvement at all.
We dont kno exactly what new to that IOSs. We know about sercurity fix but we dont know about bugfixes or anything else. I would nice to know if the compatibility to usbloaders is broken with them, some games do not work, some games work or anything else.