With scheduled exports the lowest frequency is currently monthly. I would love the ability to create quarterly reports. My use case is that we have many partners who require a quarterly update from us. The workaround I have decided to use right now is to receive the reports monthly (and simply delete them 2/3 of the time). I can imagine others have similar use cases. I can understand the quarterly/biannualy could be unique in the months people use.
So my suggestion is to include a checkbox for the months included in monthly reporting. By default it could select all months. This gives a ton of flexibility for additional reporting schedules.