Are there plans to release datasheets for these? I'm interested in using the RK1 in a custom carrier board as a more cost effective alternative to the Firefly Core-3588J.

Since the TPi2 is pinout compatible with the Nvidia Jetson (and the RK1 is designed to work with the TPi2), the Jetson pinout may be a place to start..?

The documentation is going to be released but closer to when the module itself is going to be released. If you need the documentation, yuo need to wait for a bit still.