If you have a Zetex 1.15y with four Spartan LX150, a tiny modification to the code will change it from SHA-256 to SHA-224 and it is quite profitable mining Bismuth.
This is not true, apparently you havent spent that much time looking at the code
Why not. Basically I have made a miner for Bismuth, but stopped for a while because of lack of time, of good pools and ccminer's support.
In my opinion the biggest problem could be the finalizing of solution by searching "needle" in the "haystack", as it is called in the source code. But it may be solved.
The expected keccak hashrate of single LX150 is 250...500 MH/s depending on luck and efforts.