Yeah I know this is a fairly well-trodden model recommended by FSF (okay, maybe I shouldn’t have called it kinda strange). I’m not confident it works out in most cases, though. So I’m wondering if it’s intentional in this case.
Actually, if you have other examples of this happening in the wild, I'd be quite interested.
The other widespread example I have in mind (which seems to work well) is WordPress extensions with premium features, but I've not encountered this too often neither.
Edit: thanks all for your examples :-)
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That said, I assumed it’s fairly well-trodden mostly because FSF for as long as I can remember approved/recommended something along the lines of selling builds but completely opening the source. I guess RHEL arguably falls into the camp as well, but they sell more than builds.
I believe the FSF points about selling software come from a time where you sold the medium (like floppy disks) with the software: you had to allow doing this because it was not practical to spread software without doing this and not costing (too much) to the author.
I don't really think it's practical advice for the present, they were never really business model specialists.