A frequently discussed issue with long-term archiving is software compatibility over long periods of time -- what happens when no one remembers what "Centera" means, but there's still terabyte upon terabyte of disk stored in Centera format? While the debate rages about those issues, the issue of long-lasting physical media is often overlooked. Current digital media formats are far more advanced in the short term, but in terms of readability over vast stretches of time, they've still got nothing on the Rosetta Stone.
One by one, according to Remsing, the different formats can be scratched off the hundred-year archive list for physical reasons. It's difficult to put RAID on tape and difficult to migrate between formats on any form of removable media, whether tape or optical. Disk is flimsy in the long run and requires power and cooling.
There are many ideas, like holographic disks proposed. Worth thinking about.