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