How about building a set PMOD compatible cards to take advantage of the open-source Verilog peripherals at https://github.com/DemandPeripherals/DPCore.git. The DPI people are converting to PMOD externally and to a Wishbone bus internally.
Software defined peripherals can eliminate the microcontroller from many Linux based control system. Getting rid of the microcontroller would save a HUGE amount of time for your customers.