You can buy the HiFive1 board (I have a few and they're swell), but it's more of a microcontroller than an application processor, the board is Arduino compatible. If you want something more like a Raspberry Pi or bigger, you'll have to wait a bit longer.
The Freedom Unleashed platform is coming down the pipe, and you can pre-evaluate it on an FPGA board (albeit at lower frequency, and fairly pricy since it's a complex design and requires a fairly large FPGA to prototype). I won't pretend to know when they'll have a standard Freedom U500 SoC dev board, but it will have multiple cores, PCIe 3.0, USB 3, Gigabit ethernet, and DDR4 compatibility according to their website[1].
The Freedom Unleashed platform is coming down the pipe, and you can pre-evaluate it on an FPGA board (albeit at lower frequency, and fairly pricy since it's a complex design and requires a fairly large FPGA to prototype). I won't pretend to know when they'll have a standard Freedom U500 SoC dev board, but it will have multiple cores, PCIe 3.0, USB 3, Gigabit ethernet, and DDR4 compatibility according to their website[1].
[1]: https://www.sifive.com/products/freedom/