There are two ingredients to success:
1. Coin algorithm. How compatible is it with FPGA.
2. Qualification of the programmer.
Very often, stupid programmers create an aura of impossibility of any process. Then a skilled programmer destroys that aura in a day. But a skilled FPGA programmer is expensive and usually does not deal with crypto
![Smiley](https://bitcointalk.org/Smileys/default/smiley.gif)
FPGAs are expensive and not produced in large quantities. Lots of export restrictions here too. This all complicates the development of a commercially viable device.