Are the sub-queries in CQL or are they planned?

We query for the descendants of a page using the ancestor CQL field:

ancestor = 123

So far, so good.

Now I am in a use case, where I’d like to get the descendants of multiple ancestors where the ancestors themselves are result of query, but all this with a single query. Something like:

ancestor = subquery("label = foobar")

(In this example, I’d expect to get the descendants of all page that is labelled with “foobar”.)

Is this possible somehow? With an app maybe?