TODO list request: FK to unique expression indexes

Folks,

Since it's too late to look at this for 8.4, can the following go on the
TODO list?

Referential Integrity

[] Allow creation of FKs targeting unique expression indexes on the
referenced table. Syntax: REFERENCES <reftable> ( ( column expression ) )

Reason: current FK rules do not allow creating FKs to columns which are
defined as, for example, unique(lower(column)). This forces users to
either abandon RI for that table, to store duplicate data, or create
superfluous indexes.

Hmmm ... I suppose the above would require enabling expression indexes
for PKs as well, no?

--Josh Berkus