correlated subquery quit correlation on where clause requires use keys - remove or relax limitation

Consider

SELECT (SELECT date, ARRAY_AGG(DISTINCT expiry) AS expiries

    FROM `default`

    WHERE _dataType='o2'

    AND underlyingId IN [500046, 527383]

    AND date BETWEEN firstTradeDate AND expiry

    AND expiry IS NOT MISSING

    GROUP BY date) FROM ['2018-01-01', '2018-01-02'] date

(just a query that returns all trades active on specific expiry dates, grouped by expiry dates).

This is perfectly legal N1QL, which however fails with

Error evaluating projection. - cause: FROM in correlated subquery must have USE KEYS clause: FROM default

It's not exactly clear why the limitation is there, but if I remove the check from planner/build_select_from.go:builder.VisitKeyspaceTerm() the request goes through happily and returns the expected results.

I suspect this is a relic from old style joins. It would be good if we could remove this at least for ANSI joins.