AMD is legally forbidden to use HDMI 2.1 drivers that *AMD* developed to support HDMI 2.1 features under Linux? Have I misunderstood something? Else it would mean EVERY hardware device manufacturer could legally forbid someone writing driver support for Linux, which is ridiculous. AMD isn't asking for permission to open-source someone else's proprietary code, so I don't know why the HDMI forum has got its knickers in a twist over this.
The issue is AMD has access to the entire HDMI implementation, they can't just say they developed it out of nowhere. If I reverse engineered the implementation and released an open source version of it the HDMI Forum could do fuck all about it, but AMD can't release an independent version because they have access to the original and it will always be argued they've copied some details over or based their work on it.
Hopefully in future there will be 3 DP Ports in general
That's already the case in about 90% of gpus. As far as I can remember only Gigabyte does 2 DP + 2 HDMI in some models, otherwise it's always 3 DP + 1 HDMI. I don't like HDMI but prefer the gigabyte way with 2+2 because some monitors, particularly the cheaper ones still often come with no DisplayPort ports.
IIRC it's 0.15$ per hdmi port.
The signalling itself is very different. You can't use a "dumb" cable with DP at one end and HDMI at the other. Unless the device have built-in support for sending the "wrong" signal to the other kind of output.
If the DP is in the output side you absolutely can, DP is pin compatible with HDMI and has a functionallity called Dual Mode Display Port that allows for a DP output to send an HDMI signal without any issues. Most adapters on the market exploit exactly this, they just connect one end to the other and that's that. It's why HDMI to DP adapters are always more expensive and you need to double check what you're buying.
Unless you have a "designed for piracy" splitter that spoof this. In my experience, HDCP will fail even just by using MST to display an extended desktop view in Windows on two HDCP capable displays
It's not about being designed for piracy, you can't split an HDCP protected signal but you often need to. They could spend the effort re-encoding the stream but why bother!? It also fails under DP MST because Vesa didn't bother to account for that when designing MST, and again why should they!?
The idea of HDCP is completely ridiculous and pointless, it doesn't stop you from pointing a camera at a TV and in the case of physical media, the disc encryption was broken directly years ago. The only thing HDCP ensures is that you need to buy a new equipment every couple years whenever a new version comes out.
Really lacking context. Is this of technical or political nature? Maybe the HDMI copyright protection doesn't work like it should on Linux or 
