coupling of index and table access methods

Hi hackers,

My extension introduces a new table access method together with an
index access method. Specifically, these AMs work with in-memory data.

I would like to make a CREATE TABLE request with PRIMARY KEY, UNIQUE
constraints etc, to pick my in-memory index AM over default btree when
the table is created using my in-memory table AM. Also it might make
sense to forbid using other index AM for CREATE INDEX requests against
an in-memory table.

It seems that this is not possible now without modifying the psql
core. What might be the best way to accomplish this?

Also if I implement such a thing would anybody else be interested in
it? Is there any sense to publish it?

Regards,
Aleksey