MCU's are basically locked to a vendor currently. You choose a chip, make your design around it, and hope there won't be a shortage from that vendor, and it's high enough on the vendor's priority list to not hurt your product.
If there was a RiscV chip that met a particular standard (x voltage range, y clock speed, same supporting circuitry and software), then we'd have multiple chip vendors creating the same part, and hopefully it would turn into a jelly bean chip.
I don’t see a standardized pin definition coming soon in something as complex as a Linux compatible SoC with DRAM interface - that isn’t a thing sometimes even across a single sub-class of products from a same company.
Maybe there will be a gold standard of RISC-V SoC like there was the Intel 8086, and bunch of clones could show up. That was close to happening with ATmega32U, but ultimately the clones disappeared.
More likely in an SBC with only a few buses emerging? Advantage there could be to do your high-density routing and PCB mfg with a smaller trace-width etc process.
How is that different than with ARM? There are plenty of ARM MCUs out these days and it seems like ARM's defeated MIPS for the embedded space. But once you step away from the core ARM bits it's all proprietary.
If there was a RiscV chip that met a particular standard (x voltage range, y clock speed, same supporting circuitry and software), then we'd have multiple chip vendors creating the same part, and hopefully it would turn into a jelly bean chip.