Those days are almost gone. ASICs are destroying all profitable coins step by step, from the other hand GPUs are getting better.

I think it is necessary to use external memory to make FPGA-miner profitable. FPGA without external memory is severely limited. It is also good to implement the PCI Express interface. As a result, the PCB will not be very simple.

The problem will not be in the complexity of the PCB, but in the price of the FPGA. You need a huge discount for a massive purchase in order to get a payback.

As a FPGA developer, I'm considering only high-performance solutions. They are compact, profitable and scalable. Perhaps I underestimate the potential of inexpensive modules, because I usually do a fully unrolled pipelines.But algorithms like nist5 require a folded implementation when small chips are used. So low-cost cards may be profitable.

But IMO the most interesting is solution based on top FPGA like Virtex Ultrascale+.

I will support a new thread dedicated to the FPGA.