First, and most importantly, while there are currently only a small handful of devs, you’re standing on the shoulders of giants. I haven’t done any source analysis as to how many klocs you have contributed vs not, but I’ll bet its a tiny percentage- especially if you factor in total klocs contributed over the 15(?) years of the project versus your relatively recent involvement.
Secondly, your act of “big companies should pay me or they can’t have Netatalk” shows a gross misunderstanding as to how Open Source works, and the rules the GPL binds you by. Please don’t feed the trolls with claims that there are lots of BSD headers running around source files, as some of your strawmen have been doing in various forums. That’s bunk and well-explained in historical discussions. Every line of Netatalk code is under the GPL unless you want to base “your” version of Netatalk off of versions prior to 1.5, when it was BSD-licensed.
Lastly, I’m disappointed in you. I won’t betray confidence implied in discussions we’ve had, but this isn’t something I would have expected from you. Your assertion that “it’s better to have an actively developed Netatalk, than a non-free, non-open Netatalk” is very incorrect. It is the freedom and openness that got it to the point where you could derive value from locking it up.
I’m sorry your business plan is obviously not working the way you’d like. This isn’t the solution. The solution is to change or replace your business plan, not commit at worst legal license violations, and at best very disrespectful and dishonorable acts with that which is not yours.