I have just looked a little bit around, and it seems that using ntfs-3g for writing may now be considered acceptably safe. I don't think the Open SUSE wiki entry, http://en.opensuse.org/NTFS , which has been recently edited and reviewed, would have recommended it , also for ordinary users, otherwise. SUSE is much focused on interoperability. But they advise against mounting damaged systems rw.

From the descriptions of NTFS 3.1, it seems that changes with new OS versions mostly have to do with metadata use, so while writing may imply a risk of getting impaired functionality in some respects, the likelihood of messing up the whole file system is much less. And, in particular, when using NTFS only for the KNOPPIX structure with the persistent image, almost all updating happens inside that file - which ought to minimize the risk of file system damage. So, at least, "installing" the Knoppix files on NTFS seem to be relatively safe. A small warning would still be in place at such "installs", as it is not foolproof, but I think I agree with your considerations

Edit: Fixed link, it should work now.