Currently Oak supports runtime of aggregation of content which works ok for some cases. However as noted in  it might not perform well or not give expected result in some cases.
JR2 supported index time aggregation  with following features
- Support for nodeType scoped aggregation rules
- Recursive aggregation support (
Oak should also provide similar aggregation support. To start with we can support #1. Support for #2 can be added later depending on requirements