Toasting more system-table columns

I find the following varlena (ie, potentially toastable) columns
present in the system tables:
   relname     |   attname    | typname  | attstorage
----------------+--------------+----------+------------pg_aggregate   | agginitval   | text     | xpg_attrdef     |
adbin       | text     | ppg_attrdef     | adsrc        | text     | ppg_class       | relacl       | _aclitem |
mpg_database   | datpath      | text     | ppg_description | description  | text     | xpg_group       | grolist      |
_int4   | ppg_index       | indpred      | text     | xpg_language    | lancompiler  | text     | xpg_proc        |
probin      | bytea    | ppg_proc        | prosrc       | text     | ppg_relcheck    | rcbin        | text     |
ppg_relcheck   | rcsrc        | text     | ppg_rewrite     | ev_action    | text     | xpg_rewrite     | ev_qual      |
text    | xpg_shadow      | passwd       | text     | ppg_statistic   | stacommonval | text     | xpg_statistic   |
stahival    | text     | xpg_statistic   | staloval     | text     | xpg_trigger     | tgargs       | bytea    |
ppg_type       | typdefault   | text     | p
 

Of these tables, only pg_rewrite has a toast table so far.

Offhand it would seem to be a good idea to create toast tables for
pg_attrdef, pg_description, pg_proc, pg_relcheck, possibly pg_statistic.
Certainly a toast table for pg_proc is a must so that we can deal with
large procedure bodies.  Toasting pg_attrdef would allow very large
column default expressions (dubious value), pg_description for long
comments (probably should have this), pg_relcheck for long constraint
expressions (probably want this), pg_statistic to cope with long
min/max/common values (not sure about this).

I doubt the other system tables need toast tables, although we may as
well mark all of these attributes "m", ie, they should be compressible
in-line even if there is no toast table.

Comments?
        regards, tom lane