Here at Berkeley Architecture Research and our spin-off company SiFive, we are working on finalizing version 1.9 of the privileged ISA, which includes a lot of useful features for operating system implementers. This includes a standardized way of performing memory-mapped IO, debug port, and possibility of standalone boot.
That being said, you can already use a RISC-V processor by programming the RTL onto an FPGA board. The Zedboard and ZC706 are both officially supported. Though both of these boards are pretty expensive.
When (roughly estimated) can we expect the first actual boards?
> The Zedboard and ZC706 are both officially supported. Though both of these boards are pretty expensive.
How long will these boards be supported in later versions of Risc-V / ISA? It makes no sense to purchase an expensive board unless it can be used for a long time in upcoming RTL versions.