Depending on expense, i'd look at adding a small XMOS processor to the board. It being transputer in essence was designed to talk other chips like ASICs and other XMOS. The ASIC is left doing its special magic, the XMOS handles everything else (including block submits etc.) and can be easily connected up into massive rigs as required.
They're kinda neat, fairly powerful, and the chips aren't massively expensive either. I actually have an XMOS XK-1 boards here flashing an LED at me accusingly. The caveats are that USB is a bit tricky, requiring external components and using up nearly all available I/O ports on that core (so you really need a more expensive dual core chip for that), the chip has some slightly interesting power sequencing and reset requirements, it has no internal Flash so you need a seperate SPI Flash chip for firmware, and it has no internal driver for a crystal oscillator. (
Edit: oh, and you're limited to 64 kilobytes of RAM per core and your code needs to fit into that too.) An ARM microcontroller with integrated Ethernet MAC and USB might work out better.
Of course, there'll be some tricky board design and manufacture anyway for the ASIC, so that may not necessarily be a huge obstacle.
Edit 2: Also, a totally untested 90MHz/90 MHash/sec bitstream for the DE2-115 is now in a branch on my git repo. PowerPlay estimates 4.4W of heat, I think? Anyway, don't blame me if you blow up your expensive board. There's a reason I'm not including instructions here.