The big players in the Wi-Fi SOC market are all using ARM in recent designs, Intel and its multi-core Atom being an exception. RISC-V isn't supplanting these at the moment. The chipsets in this market are highly specialized: most of the network functionality is offloaded to proprietary hardware peripherals, and the CPU is mostly only doing control plane and bookkeeping. Given the low margins of these products, some designers may eventually drop ARM for RISC-V, but there is a lot of inertia: designers are
far more concerned with keeping up with fast-changing wireless standards and delivering new features. The marginal cost saved replacing these small, slow, low-cost, low-power cores isn't a big priority, especially given any risk of delaying new products.
I suspect there is plateau coming in the foreseeable future, as all the most desirable spectrum is fully utilized by maturing chipset designs. Should that happen, cost reduction will become a higher priority.