Nice idea. Are you following this work by Katsuhiko Inoue?
A good first step with this is to plug two THETAs into one Raspberry Pi and see if the Raspberry Pi can find both cameras with libptp over the USB cable.
I think a good first step would be something like this on Raspian:
Verify Computer finds Camera as USB Devices
Bus 003 Device 009: ID 05ca:0366 Ricoh Co., Ltd
Verify ptpcam Can Connect to Camera
First verify that ptpcam can connect to the camera.
$ ptpcam -i
Model: RICOH THETA S
manufacturer: Ricoh Company, Ltd.
serial number: '00010093'
device version: 01.42
extension ID: 0x00000006
extension description: (null)
extension version: 0x006e
This thread indicates that it's probably possible.