I'd certainly be interested in two, one for an A500+ and one for a CDTV (depending on the price.)
Is it a one-time programmable FPGA? Or can it be reflashed via JTAG?
FYI the Atari ST's equivalent to the Gayle IDE controller is called the "ST-Book IDE controller" and AFAIK a re-creation of it is part of the opensource SUSKA project. As is the Atari Memory Map.