BRIN indexes and ORDER BY

Hello,

We're curious about the current behavior in 9.5.4, and possible future
enhancements, of BRIN indexes with respect to ordering.

In the docs, section 11.4. "Indexes and ORDER BY" (
https://www.postgresql.org/docs/9.5/static/indexes-ordering.html) is clear
that anything other than B-tree indexes have unspecified ordering:

"In addition to simply finding the rows to be returned by a query, an index
may be able to deliver them in a specific sorted order. This allows a
query's ORDER BY specification to be honored without a separate sorting
step. Of the index types currently supported by PostgreSQL, only B-tree can
produce sorted output — the other index types return matching rows in an
unspecified, implementation-dependent order."

We found a pgsql-hackers thread from about a year ago about optimizing
ORDER BY for BRIN indexes. Tom Lane suggested that he was working on it:
https://www.postgresql.org/message-id/11881.1443393360%40sss.pgh.pa.us

Our current test shows that ordering by a BRIN indexed column still
performs an unoptimized sort:

SELECT generate_series(1, 10000000) AS id INTO test;
CREATE INDEX idx_test_id ON test USING BRIN (id);
EXPLAIN SELECT id FROM test ORDER BY id DESC LIMIT 20;

Limit (cost=410344.40..410344.45 rows=20 width=4)
-> Sort (cost=410344.40..435344.40 rows=1000000 width=4)"
Sort Key: id DESC
-> Seq Scan on test (cost=0.00..144248.00 rows=10000000 width=4)

Is there anything we're missing to speed this up? Or is it still a future
feature?

Thank you,
Darren Lafreniere