DRM+ broadcasts digital audio over medium, short, and also long wave. It has 30 - 180 kbit/s depending on coding, in a 100 kHz channel.

Using 10 or 50 kHz down there as a data broadcast channel would not be an issue, as it's not like the longwave band is exactly crowded.

Have you ever listened to VLF with a good receiver and antenna? It is chock full of signals.

Sadly, it appears that many of the beacons are going away: https://www.dxinfocentre.com/ndb.htm