Intel owns patents on the Itanium ISA and aspects of the x86 ISA. If you still think instruction sets can't be patented, just try challenging Intel about it in court. There will be a smouldering crater left where you once stood once the lawsuits are over with.
This is simply false, as far as Intel is concerned. You can't even emulate x86 (therefore infringing 0 hardware patents) without expected heavy litigation from Intel.
AFAIK the actual x86 patents have expired but none of the extensions have (x86-64, SSE, ...)
> "Intel naturally tries to threaten and extend patents as much as they can. But they ISA itself can't be patented."
It is practically impossible to implement these extensions, such as SSE variants, without intel being able to make a case against you. So even if theoretically the ISA can't be patented, for all practical purposes they have the legal power to effectively prohibit a 3rd-party from implementing an x86 core.
RISC-V will have less problems with those kind of patents, but it's impossible to design high-end microarchitecture without cross-licensing.
I may sound negative, but I'm actually positive about RISC-V in embedded and IoT arena. People just attach too much hype for the architecture.