I've just spotted some work I need to get done in the next 7 months. 10 digit ISBNs are being phased out, in favour of ISBN-13s.
Admittedly, it will simplify things, since the ISBN-13s will initially have the same 978 prefix, and the same check digit calculation, as is currently used in the barcodes, thereby meaning that the ISBN above the barcode and the number encoded in the barcode are the same.
And in a few years, they'll start using the 979 prefix, too, doubling the currently available number space.
Looks like Amazon haven't caught up with this one yet.