It's been relatively difficult for me to figure out what is really going on here. It is well-known that the Free Software Conservancy has been actively enforcing the GPL on Busybox. But then, at the same time gpl-violations.org has been (and still is!) similarly active in enforcing the GPL on the Linux kernel. Still, I haven't yet seen calls to write a non-GPL Linux kernel replacement. Of course, the complexity is on an entirely different scale, so this point is moot.
However, for quite some time there have been rumors about the intensity (some would say aggressiveness) of the enforcement. I don't want to accuse anybody of anything, so I'm going to write speculatively about it.
This post is to summarize my thoughts on all of this:
It is well within the right of each author / copyright holder to decide on the enforcement strategy and license interpretation. As such, I respect the decision of the authors. It is their work, they should decide what to do.
In any kind of GPL enforcement, you of course not only want the complete corresponding source code to one program, but to all of the GPL/LGPL/AGPL or otherwise copyleft licensed programs contained in the product. We at gpl-violations.org have always been requesting the complete corresponding source code to all GPL licensed software during our communication with the infringing companies. This request was typically honored by everyone, without the need to apply any pressure onto it. After all, releasing only one bit of code causes the risk to get sued by somebody else who owns the other not-yet-compliant part of the code.
Now there have been rumors that SFC was not only requesting non-Busybox source code, but also making it a condition for the explicit re-instatement of the license on Busybox. Whether or not there was such a hard condition is subject to debate and there are different opinions on it. For those in the field of FOSS licensing, it has always known that there are different lines of thought with regard to the requirement to explicit reinstatement. We in Germany generally think that it is not required at all, and the existing preliminary injunctions at least implicitly acknowledge that as they enjoin companies from distributing a product as long as it is not in compliance with the license. In other (particularly the U.S.), it is generally assumed that explicit reinstatement is required. In such a case, it may very well be legally possible to use it as a lever to obtain source code for other programs like the Linux kernel. However, I am personally not sure if that really is the right strategy. Not everything that is possible legally is ethically the right thing to do. But then, ethics and legal customs differ widely in the FOSS communities, as they do in society in general. Some countries and communities believe in the death penalty, others don't. Some countries allow abortion, others don't. Some allow prostitution, others don't. So when judging about whether that "reinstatement lever" is acceptable or not, we have to accept that there may be different lines of thought. I for my part definitely think that the far superior method is, beyond doubt, to have a rights holder on those other program in order to make any demand for source code (as opposed to a mere request without implicit or explicit legal threat).
There also have been rumors about a requirement on submitting future source code releases to a compliance audit by the Conservancy. According to SFC sources, there never was any such demand, and the rumors are likely spawned by some incorrect claims of a defendant in a court case, which ended up in the public record. If there was such a requirement, I wouldn't think it is just - at least not for a first-time non-intentional infringement case. If there was repeated infringement and a clear sign that it would happen again and again, such a requirement for future audits may be justified, depending on the case.
People who claim that GPL enforcement is scaring away companies from using Linux and/or other Free Software also have to be careful in what they say. If a commercial entity enters a new market (let's say Android Tablets), then there is a certain due diligence required before entering that market. So if you don't understand Free Software and particularly GPL licensing, then you shouldn't place a Linux-based device on the market. Just think about an analogy: If you have a recycling company and enter a new market (disposal of hazardous chemicals), then you cannot simply treat those chemicals as regular waste, wait until you run into legal trouble and expect to get away with it.
I think there are still far too many GPL violations out there, and we need to see more enforcement in order to get all the major players in their respective lines of business into compliance. But come on, dealing with embedded devices in 2012 and still getting compliance outright wrong really means that there has not been the least bit of attention on this subject. And without enforcement, it is never going to change. People who want no enforcement should simply use MIT-style licenses.
Last, but not least, I also think GPL compliance is a matter of fair competition. There are some companies who really do a good job in ensuring compliance with the various Free Software licenses. If their competition doesn't invest the funds into the respective skills, procedures and business processes, they are getting an unfair competitive advantage against those who are doing it right. If there was no enforcement, the motivation would be to reduce efforts in compliance, not increase it.
Let me conclude with a clear statement to anyone who thinks that by replacing Busybox with a non-GPL licensed project they can evade GPL enforcement: It will not work. There are others out there enforcing the GPL. Last but not least gpl-violations.org. Despite the notoriously outdated webpage, we are still alive and kicking, churning down on the violation reports that we receive. Armijn Hemel, Joachim Steiger, Tim Engelhardt, Julia Gebert and Till Jaeger deserve much of the credit for all that work, while I'm mostly spending each awake minute hacking Free Software for mobile communications. Yes, we should publish more about our activities, and I hope to find the time to do so. There should at least be an annual report with the number of cases...