I am saying it makes no financial sense. The major GPU coins already have asics, with ETH being the biggest. And those coins that have no asic on it will have asics on it before the FPGA will come close to ever breaking even.
And everytime an asic takes over an alternate coin, all the GPUs and FPGAs that were mining that coin will go to a non-asic coin. That means the remaining non-asic coins will have difficulty skyrocket and guess wat, that means your GPUs and FPGAs mining make less money. Everytime a new asic comes out, the FPGAs make less money. So, there is no niche. There is a limited amount to be earned from mining u see. If the asics keep appearing to take some of it, the switchers (FPGAs/GPUs) will have less and less.
Why not u calculate how much it would cost to make an FPGA that can do the equivalent of mining 504mh like the L3+ or 14TH like the S9.
Run your numbers and see the gap. While I dont have the numbers, I dont think it can work.
Anyways, good luck in your endeavors. Maybe I am wrong.
Just my 2 cents
There is no point in comparing FPGAs to ASICs using Scrypt and SHA256 as examples. That train has sailed... but until ASICs are made for the more obscure algorithms - FPGA can rule there. It takes time and millions of dollars to develop ASICs.
Following your logic, GPU mining makes even less sense, because they are "inferior" against both FPGAs and ASICs. Yet it has been quite good for many years.
Then there are various possibilities of forks, specific FPGA-friendly algorithms etc...