I think it's unlikely to be a patent issue. More likely a contractual one. If you sign up to the HDMI Forum to get access to the spec, you will have to sign aw

I think it's unlikely to be a patent issue. More likely a contractual one. If you sign up to the HDMI Forum to get access to the spec, you will have to sign away certain rights. Those contract terms will have been put in place by the same people who think HDCP is a good idea. If that's the case, someone needs to either leak the spec or reverse engineer the driver. One or the other will happen eventually.