Probably 2 weeks from the moment someone gets the bright idea to spend next couple of weeks writing code for a device to mine (probably) less than 5 MH/s @ $8
9IMHO the 5 MH/s and 2 weeks is me being optimistic.
Edit: Corrected typo. the usb thing is $89 not $8
I floated the idea on the Mojo board forums (uses Spartan-6 XC6SLX9)
http://forum.embeddedmicro.com/viewtopic.php?f=3&t=68There's interest, but at the moment, it seems as though the XC6SLX9 just doesnt have enough resources for the full design.
This was referencing
https://github.com/progranism/Open-Source-FPGA-Bitcoin-Miner That being said, some cleanup could be done around the serial comm design code included the OSFBM, and the serial comm for the mojo... but I doubt that alone would be enough to get the design small enough.
... I'd love for someone to prove me wrong though and get a working miner on it

Edit : lol hadn't looked at
https://github.com/kramble/DE0-Nano-BitCoin-Miner/tree/master/Xilinx_LX9_hashers_6 yet...