there are a few pins spare....... Just tag on a serial port... 5 minute job....
Yah, but be careful with voltage levels. Connecting to a full voltage RS232 is going to fry the fpga instantly. You'll need level translation (even for a 5V TTL port). The serial protocol is customised too (and fixed at 4800 baud to work with a minimalist opto-isolator circuit), so its not just plug and play here. Then again if you're buying an fpga development/educational board you should expect to have to put some effort in
Oh, and to repeat, its only 5MHash/sec, or 2.34MHash/sec or whatever. Just a toy which will mine you some dust only.
[Edit] Clarifcation, by "you" I mean "you dear reader", not "you razorfishl" as you're clearly far more knowledgeable than me!!
I would hope that anyone with such a board has a least the commonsense to realize that FPGA generally don't fair well if you shove 5v up the tootsie ;-)
Personally I aim for Virtex5 Virtex6 of Spartan6 , but in about 2 more difficulty changes, they will also have the same ROI as the 300MH/S usb whit-less wonder bait.
The sad thing is that in the distant past...... even the XC6SLX9 would have provided a decent income.