Currently is not possible to control sort columns for \d* commands. Usually schema and table name is used. Really often task is collect the most big objects in database. "\dt+, \di+" shows necessary information, but not in practical order.
Instead introduction some additional flags to backslash commands, I propose a special psql variable that can be used for specification of order used when some plus command is used.
some like
set EXTENDED_DESCRIBE_SORT size_desc
\dt+
\l+
\di+
Possible variants: schema_table, table_schema, size_desc, size_asc
