I think you're putting the cart before the horse.
Pretty much any computer can host a USB FPGA or ASIC miner, even a rooted Android device with an OTG cable and BFL's Android mining software.
The trouble is that as more and more ASICs are shipped and as difficulty skyrockets, FPGAs are rapidly becoming obsolete.
That leaves ASICs as the only practical solution and waiting lists are so long as to make them a questionable investment at today's prices if you have to wait until difficulty is in the hundreds of millions to get delivery.
So, it seems like you are telling me that it isn't even worth investing in any mining upgrades?
Unless you can somehow get a really good deal on an ASIC miner with a delivery time in weeks rather than months, it's borderline at the moment.
I paid $650 in February for 30GH/s worth of BFL ASICs, and I'm worried about breaking even because difficulty levels have gone parabolic with all the ASICs shipped recently.
Now they want $1250 for 25GH/s and are talking about not shipping any new orders before next year.