Yep I also think FPGA solutions and Classic hardware could go very well together.
What I'd really like to see is some FGPA projects that have an (open source) active developer community behind them to continually improve the performance.
Other possible projects:
Clock-port/Zorro 16bit mp3 decoder AHI sound cards
Clock-port/Zorro USB cards
Lisa replacement/enhancement board to provide chunky modes and RTG support (like the Indivision ECS but community supported)
Alice replacement/enhancement board to provide improved IDE speed (with a SATA or CF interface built in)
All dreams but you never know what will happen