Problem with RISC-V is exactly what makes it strong. The lack of verified software ecosystem will keep it from being main stream for at least a decade(something that until recently has held back the Arm server market, well, that and not having a reasonable server core..fixed with the ThunderX2). The fact that you can add instructions quickly is another problem, well, that and the lack of a standardized verification suite for the ISA so that software devs know that implementations are up to spec when they write code for them. I can definitely see RISC-V accelerators taking off though, driven by a more stable x86/Arm/Power core. To me, that path for RISC-V makes a lot of sense.