There are already a handful of people mining altcoins with fpga´s, and they are getting insane hashrates. Only downside is that they don´t release their bitstreams to the public.
Why should they release their bitstreams to the public ? They become nothing for it !
Psst... "become" doesn't mean bekommen.
They do receive something. A nice and beefy dev fee. Look at the total ETH hashpower for example, assume 80% of it is mined using Claymore's miner and take 2% thereof (his fee).
Do the math.