If you missed it, like two weeks ago RISC-V support was merged into upstream for linux.
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=b293fca43be544483b6488d33ad4b3ed55881064
The HiFive1 is more like an arduino, so I don't really have a use for one. The company behind it has a quadcore 64bit version which is capable of running linux but it's proprietary. I think a development board for it is coming out sometime next year, though you can buy the verilog for it for the low low price of $595,000.
For a RISC-V SoC for running linux, right now I'm keeping my eye on lowRISC who are trying to make a free implmentation of a chip to run linux on.
http://www.lowrisc.org