I could see how the inclusion of BTFS in FreeBSD might promote free software, and its inclusion would not be prohibited by any version of the GPL.
But how does the use of GPL code in a proprietary project, as would be the case in your consulting example, benefit free software? The whole point of the GPL, any version, is to make sure that derivative work is itself free software. It's not that GPL "sounds good on paper" and in reality, it's totally different.
GPLv3 on paper: You can't use it to make proprietary software. You can't use it to take away users' freedom.
If BTRFS was included as GPL code in the FreeBSD kernel by default it would taint the entire kernel and it would become a GPL governed piece of work...
There is a reason why ext2 for example isn't enabled by default in FreeBSD and why it is mostly stagnant in the tree. Nobody wants to touch it with a 10 ft pole...
Use of an LGPL library would make my life easier, also in the past when I have done work with LGPL libraries (and BSD/MIT and other licenses as well) I have contributed back bugfixes, or new features that benefit said library. When companies shun the GPL and LGPL the same benefits are not available, there is no choice for the corporation to use it and or give back, it becomes a requirement, even if it means that part of our secret sauce now because not so secret.
Good luck getting that past management.
Forcing someones hand is not a good way to start a mutual beneficial relationship.
But how does the use of GPL code in a proprietary project, as would be the case in your consulting example, benefit free software? The whole point of the GPL, any version, is to make sure that derivative work is itself free software. It's not that GPL "sounds good on paper" and in reality, it's totally different.
GPLv3 on paper: You can't use it to make proprietary software. You can't use it to take away users' freedom.
GPLv3 in reality: See above.