As far as I am aware livecd-creator will make a Live image out of any
repository you give it, this includes updates repository.
Given the manpower we have that may be the practical approach. I
would suggest
that the target is that being able to do a live image respin with the
updates repository enabled should work. If the project decides that this
must work, we could add retesting one or more live images to the critical
path update tests. I don't think this is a good idea now, but maybe someday.