I think that the intention is to support fields even if pseudohashes are abandoned. From "Programming Perl" 3rd Ed., P257:

Pseudohashes are a new and relatively experimental feature; as such, the underlying implementation may well change in the future. To protect yourself from such changes, always go through the fields module's documented interface via its phash and new functions

This is also the migration method proposedby the Perl6 RFC: Pseudo-hashes must die!.

--
John.