fillfactor for toast tables is useless?

With reloption patch, we can set WITH options to toast tables.
However, fillfactor for toast tables is useless, no?
(autovacuum options will work as expected, though.)

Tuples in toast tables are never updated. When the main tuple is updated,
old toast tuples are deleted and new ones are inserted. Even if there are
some freespaces in pages of toast table, they are never used by inserts.
I think we should not allow users to modify fillfactor for toast tables
and it should be always 100%.

We could optimize a delete+insert operation for toast tuples to one update
when the number of chunks are not changed by update.
Fillfactor for toast tables will be only useful after the optimization.

Regards,
---
ITAGAKI Takahiro
NTT Open Source Software Center