RISC-V Hits 25% Market Penetration as Qualcomm and Meta Lead the Shift to Open-Source Silicon
(markets.financialcontent.com)
SteamDeck 2 will still have an ARM.
Of what little I know, ARM core designs should be relatively easy to repurpose for RISC-V ISA, once the set of extensions normally used becomes certain. Most of the work being in decoders.
So it just comes down to a still new and not entirely stable ISA. Like with network protocols.