Honestly, I think it’s going to be quite a while before we see something cost competitive with the Pi. Sure, you can produce a board with a RISC-V core and all the trimmings, but the Pi was built on the back of sunk costs which had already gone into mass-producing, and supporting, ARM SoCs for mobile phones for roughly a decade.
I’m almost certain something Pi-like with a RISC-V core will emerge, and probably sooner rather than later, but I don’t think it’s going to arrive until there have been a few large projects by some large industrial players. The Western Digital announcement was exciting for this reason, even though I don’t have any particular interest in storage devices, because they’re helping lower the price of admission for everybody (as are SiFive, of course!).