While this is awesome, it's trained on MUSDB18-HQ which as far as I can tell is proprietary. zenodo.org claims it is available, however I have filled out their "request access" page a half-dozen times. Does anyone know of a training data-set that's possible to obtain?

Here is the zenodo response:

Your access request has been rejected by the record owner.

Message from owner: no justification given

Record: MUSDB18-HQ - an uncompressed version of MUSDB18 https://zenodo.org/record/3338373

The decision to reject the request is solely under the responsibility of the record owner. Hence, please note that Zenodo staff are not involved in this decision.