This is different, netfilter had presumable only a single copyright holder (or a few), Harald Welte.
It has many contributors. While Harald is only suing for his specific parts of code, on a practical level, there's enough of his code in the core Netfilter to make it practically unusable if it were to be removed.
Well, it is a bit different in the case of Netfilter, Haral probobly wrote most of the bits, it is kinda hard to claim that FOO wrote most of the bits for Linux.
This isn't the case with the whole of Linux. For each infginged part, you would have to figure out who the copyright holder is, and ask them to sue. Something that is infact a practical impossibility.
If you're talking about getting *every* copyright holder to sue, then I agree. But you don't need everyone, only a few key people who have code dotted all over the place. Let's say, for example, Alan Cox sued. He has code (and by inference, copyright) throughout many parts of the kernel. To remove his code, and his code only, and still have a usable kernel, being realistic, I can't see it happening.
Maybe, maybe not. One would also have to prove that Alan Cox wrote the changes he claims to have written, since older Linux versions do not have a detailed ChangeLog this is hard (and I strongly doubt Alan can remeber each line he wrote, I can't even vouch that I wrote some files on my computer, which have my named attached!). Should be easier nowadays with a VCS and those write-of's.
=46rom memory, at least one has gone to court, at least to a preliminary injunctive stage. I don't know the specifics of how things ended, except that the company in question relented, released the modifications under the GPL and made some payments to someone somewhere as redress. the details are, I'm sure, available on gpl-violations.org if you're interested.
I couldn't find them, the web page seems a bit adhoc. :-( Does anyone have a direct link?
Cheers.