There's an as yet unconfirmed rumor going around that Sony "has chosen to discontinue the commercialization" of its Marlin ebook DRM. Supported by Sony DADC, this DRM was an ideal solution for any provider that needed a secure system more than it needed compatibility with other platforms (an internal corporate library, for example).
And according to Actualitte, Sony is giving up on this DRM.
At this time, Sony DADC, which we were unable to reach, has chosen to discontinue the commercialization of its DRM. For now, it is unclear whether the choice is final, or whether other operators will take up the torch. Indeed, some had expressed the wish, but since Frankfurt no news of the project.
The lack of activation of licenses would justify, according to our information, the discontinuation of marketing. In Italy and the United States there has been some interest, but not enough to make this somewhat agnostic approach stand out.
As of yet I am unable to confirm this rumor. While I have not been able to reach Sony to get a statement, I did ask Bluefire, one of the ebook tech companies that license the Marlin DRM. They were not aware of any change in its status.
I can't see that very many companies have licensed it, though; the last was eBooks2Go, in May 2018, and before that there was ArtaTech, which added the Marlin DRM to its ereaders, and Datalogics, which integrated Marlin DRM into its Active Textbook ebook offerings in 2016.
There is in fact so little adoption that Sony DADC may indeed be giving up on the DRM, but there's no way to confirm that detail at this time.