He approves of developers selling GPL exceptions. He doesn't approve of buying GPL exceptions*. It's a subtle point.
(The natural corollary to this is that if the Element/Matrix folks—or anyone—were to ask you for a CLA excepting them from the project's own open source license, then you could/should feel comfortable kindly requiring them to pay you for it—a response which should be the default in the open source world, although it unfortunately is not.)
Personally I’m happy to ask them to kindly maintain my new feature along with all of their other code, so I can continue to use an up-to-date version with very little effort.
Almost as unhappy as if the upstream project failed and went away completely.
And in reality it depends a lot on my level of contribution. If I have dozens of lines of code in a big project, then who cares, all I really wanted was for my pet bugs to get fixed.
If I contributed major features or thousands of lines of code there, then I would be very mad. But I would also be very capable of maintaining an open source fork of the project.
(The natural corollary to this is that if the Element/Matrix folks—or anyone—were to ask you for a CLA excepting them from the project's own open source license, then you could/should feel comfortable kindly requiring them to pay you for it—a response which should be the default in the open source world, although it unfortunately is not.)
* i.e. so you can make proprietary software