I had a talk with one boy about development in plpgsql. He uses table's functions. More times he uses returns types based on some table type + few attributes. Now he use a ugly hack - he create a view on table plus some columns - and then he use the view related type as table function result type. For similar uses cases there can be interesting to have a possibility to create types by extending other types. Probably almost all functionality is inside now - so it should not be hard work.
My idea is implement inherits clause for CREATE TYPE command.