Hey Alex,
(srfi 146 hash) has an implementation now (not in the main repo, though).
A library (you proposed to name it "(srfi 146)") that exports both ordered and hash maps at the same time won't probably be imported very often, so I don't think it is important to specify such a library.
The current state of unbalanced library names will go away as soon as SRFI 146 becomes a part of R7RS-large (the SRFI proposes to name the two libraries (scheme mapping) and (scheme hashmap)).
The current (unbalanced) names have historical roots. In a previous iteration of this proposal, (srfi 146 hash) was optional.
If you think it is really important to be able to import (srfi 146 mapping) or (srfi 146 ordered), I could add such a library name to the spec and would alias it to (srfi 146) so that the SRFI remains compatible with its previous iterations.
Best,
Marc