> I think this is too convoluted.  Just keep a flat list of library names
> and don't worry about how long they are.

Name length is not the problem; it's that one SRFI can be exposed under
several library name prefixes. E.g. (srfi 1), (srfi :1), (srfi :1
lists), and (scheme list).

This is not usually such a problem, but for SRFIs with lots of
sublibraries like 160 there would be a four-fold repetition of all the
names.

> (srfi 146) and (srfi 146 hash)
> both exist, but (srfi 160) does not exist.  That allows us, for example,
> to add (scheme foo bar) to an existing (scheme foo) even though they
> happen to come from different SRFIs.

Yes. I mistakenly wrote (sublibraries () ...) in the SRFI 160 example.
It should be missing the ().