That method is documented to return unique IDs, but fails to specify how
different entities can guarantee that they do not create clashing IDs (e.g., by
providing a registry of unique prefixes, so that each entity uses another
prefix; see issue 32547 for a similar problem).

The only client of getImplementationId seems to be BASIC (ab knows the details),
where uniqueness of IDs seems indeed to be required.

Also, at least the implementation of getImplementationId in
jurt/com/sun/star/comp/loader/FactoryHelper.java 1.7 does not generate unique
IDs, as it uses hashCode (also see issue 32546).  (And, as discussed with ab,
returning an empty sequence from getImplementationId, as is probably done in
many places, is not a solution, either, as it will incur a performance hit in
the BASIC use case.)