I managed to recover about a hundred 20 MB Bernoulli cartridges one time. The OS ain't the problem.
Actually, one of the biggest problems, IMHO, is going to be determining what material is worth moving to newer formats. Even if it only takes ten seconds to convert the contents of a floppy into modern format, what is somebody with a bunch of floppies and no particular clue what's one them supposed to do with them? One of the advantages of printed material is that in many cases one can pick up an item, look at it, and have some clue what it is. Even with movie film that can be somewhat possible if one has good eyesight (much easier with 35mm than 8mm, though!). Another difficulty--and this applies not just to computers but to all types of material--is the loss of metadata. A computer may be able to tell that a file contains a picture, and a human may be able to tell that it contains a picture of a woman holding a baby. But who are the woman and the baby? If there isn't anyone around to identify the significance of a picture, that significance will be lost even if the picture itself remains.