This was discussed in #289 (comment).

We could add support for a new query parameter ?indirectExpand that will allow eager loading non-directly related collection records within a single client request.

It should work similarly to the existing ?expand parameter but with additional 2 extra prefixed keys that points to the related collection and field (an additional finalizer prop key may also be needed in case of duplicated indirect expand fields from different collections).

The format in the related discussion is not final and may change after we start working on the issue.