The legality of x86's ISA being copyrighted/patented aside, the x86 ISA isn't that attractive for any new endeavours. It's a very complex ISA which is incredibly difficult to decode. Internally, it is anyway converted to RISC style microops. So as a competitor, you don't really gain a whole lot by implementing the x86 ISA apart from the ability to run software without writing a new compiler. What's more important is the microarchitecture.