Several people in the community (myself included) are working on open-platform FPGA miners (stock FPGA cards widely available + publicly released bitstreams with 2% fee). The ROI right now is 15 to 90 days based on the card and the algorithm. In my mind open platform FPGA mining will soon replace GPU's for altcoins, and the FPGA's are almost immune to forking.
Any links or references to what you're talking about? Unfortunately some of us don't live in basements or geek out all day so we may not easily understand what and how FPGAs work for mining. My guess is that if ROI is 15 to 90 days as you say, it won't ever be available to the public until that number rises. People are greedy and developers will want to keep profits to themselves first.
I know the ROI since I am developing for the boards myself, but someone else also posted they were yielding similar ROI's for their FPGA project. My algorithms are not finished yet, but all the high end boards are available for purchase immediately. The hardware is available, the software/bitstreams will be available relatively soon. I considered just mining with it and keeping it secret, but giving it away and charging a 2% fee ultimately yields more money in the end, so everyone benefits.
If you want to understand the technical side, consider that each core in a GPU is a serial processor capable of all sorts of math, and each math function is on a different part of the core. Since only one math function is done at a time, then technically 80% of the GPU is actually 'idle' (all functions that are not being used in that particular instant are idle). An FPGA that is programmed for mining is utilized 100%, that is to say that no single part of the chip is ever idle, every part is always working. So even though the clock speed of the FPGA is lower (300-600MHz) than a GPU, the hash rate is drastically higher.
