I honestly wouldn't expect to see any computer support DSD over HDMI as it's not possible to get DSD over HDMI working from any computer whether it be a PC, Mac, Raspberry Pi, etc.
It's impossible currently, only because the device manufacturers haven't implemented the feature, for whatever reason. Those reasons have not been made public.
It would make sense if SACD discs could be read on a computer via an attached optical drive that supports SACDs, but this has never really happened with any commercially available optical drive for a computer.
There are several web sites that offer DSD music downloads also. Acousticsounds, NativeDSD, Sony. So, I don't think the fact that SACD has copy protection and can't be read on a PC optical drive is a good reason for video cards not to be able to transmit DSD.
Supporting DSD over HDMI from a computer would require driver support added by the graphics vendors (whether it be Nvidia, AMD, Intel, etc.) or support in the open-source graphics drivers (e.g. Mesa on Linux) or whatever is handling the HDMI output.
Yes. And it seems that it wouldn't be that hard to add the feature if there was a will. And AVRs have supported it for a decade +. DSD support was added to HDMI version 1.2 in 2005.
Finally, there might be some issues implementing DSD support in drivers as it's owned by Sony/Phillips and a) adding support would require expensive licensing, which AMD/Intel/Nvidia isn't willing to do or b) anyone implementing it without licensing it could potentially be sued over it.
Hard to imagine that just passing bits through the interface and flagging them correctly as DSD would require a separate license. At the HDMI level, all copy protection is handled by HDCP, which is already supported by all GPU vendors and most SOC makers for single board computers.
I did a bunch of Google searches and could find no evidence of any DSD licensing requirement. I think if we were talking about the SACD copy protection, you might be correct. But not DSD which is based on patents that are all long expired.