Generalized Inverted Generalized Search Tree

We can index multiple scalar values per row with GIN access method,
and also can index single vector value per row with GiST AM.

Is it worth having a new AM to index multiple vector values per row?
It will be an AM for the missing feature in below:
               | scalar | vector |
----------------+--------+--------+single per row | btree  | gist   |multi per row  | gin    | *HERE* |

We can call the new AM "gigist". Or, there might be another idea
to support expression indexes for SRF functions, like =# CREATE TABLE tbl (c circle[]); =# CREATE INDEX ON tbl USING
gist(unnest(c));
 

Comments and ideas welcome.

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