The use of ":" was discussed at length during the draft period of SRFI 97. I didn't say that the mapping using ":" as a prefix is unnatural.
Apart from being arbitrary, ":" maps very unnaturally to file names.
I don't think there is a need to break backward compatibility (with established schemes) gratuitously.
What matters is the whole "ecosystem". We install some Scheme implementations and some library files. The former shall find the latter. There is no established standard on this level, just special cases for each implementation.
There's no sensible way to handle the mess without fully customizable loaders which are at liberty to fully rewrite any library name. The ":" prefix is not the only problem, and there are sure to be new unforeseen problems in the future. RnRS can never solve this stuff; it'll be behind the curve no matter how many hacks are standardized.
The requirement that every library name has at least one identifier doesn't pose a problem for the above.
