You might as well just have whatever normal for-pay license. The reason it is an issue is that not just that it's not legitimate GPL (which is ethically wrong to me- it's literally stealing from a community).
The issue is that it splits up the repos which messes with the upgrade structure. That's fine until you get a security issue and the community can't collectively update to mitigate the issue until the people using the software have paid for their liceneses.
To your point about rebranding stuff, people do that but it's not discussed often in the community. Personally, I feel like white-labeling people software sounds like a community service.
But there really isn't any money in that and it's shunned by the community, so you get a lot of malware created (which is, once again, a problem created by the culture around selling GPL software as if it were closed-source).
Anyhow, other than a few large plugins, the people making real money in the space are doing custom work and leveraging the open source, which is the "real" solution and what folks are doing in other ecosystems as far as I can tell. There are plenty of folks making money off "commercial" WP plugins, but IME that's not the main source of income into the economy around WP.
