[snvzz]

>You still have to design the cores and that's the really hard part, moreso than designing the ISA.

Designing them is an option. RISC-V's license allows doing so. But, unlike ARM, where your only alternative is to license ARM's own designs, in RISC-V there are several options.

You could use open source cores, or license cores from someone. As there's an open market of cores, there are several competing companies, offering several competing cores and support arrangements.