I'm not much of a RISC-V guy, but using the arch doesn't require you to open up your design (the arch is basically BSD). So, someone who puts the effort into making a super fast risc-v core will still have an advantage over most everyone else as the effort required to create a fast core is a lot different from the effort required to just get something that works.

So, the devices can't just be "cloned" without the RTL/etc for the design, and even if someone got some masks or the RTL via an illicit source it would still be copyrighted enough to keep them from selling the clones..

Of course if "clone" means you spend hundreds of millions of dollars building your own competitive core, then yes that is still allowed..