There has been a lot of talk about companies and individuals adopting licenses that aren’t OSI opensource to protect themselves from mega-corp leechers. Developers have also been condemned who put donation notices in the command-line or during package installation. Projects with opensource cores and paid extensions have also been targets of vitriol.
So, let’s say we wanted to make it possible for the majority of developers to work on software that strictly follows the definition of opensource, which models would be acceptable to make enough money to work on those projects full-time?
Premium support channels - This is basically how RedHat and Canonical make their money, while offering FOSS for individuals.
Donations - KDE and GNOME are largely donor-backed, both by individuals and corporate entities.
Commissions on features - Collabora for example is commissioned by Valve to improve KDE and SteamOS.
Software licenses - Certain FOSS licenses may permit paid access to software as long as the source is open i think? There are also source-available eg. Asperite that are open source, but only offer binaries for customers.
Add on services - Your FOSS web app can offer paid hosting and management for clients. Your distro can offer ISOs with extra pre-downloaded software for a fee (Zorin). You can partner with hardware to distribute your software (Manjaro, KDE).
Hired by a company to work on your project and integrate with their own stack. This is what Linus Torvalds did with Linux when he was first hired by Transmeta - part of his time was spent working on Linux to work better with the technology Transmeta used.