Who pioneered this? Was it TrollTech with Qt? (Author mistakenly calls it QT.) Or actually FSF themselves?
A disadvantage is that it goes against collaboration of people who don't profit from the proprietary version. They need to dual license their contributions by assigning their copyright to the organization (as FSF also requires). How many people refuse to collaborate as a result of this?
The canonical "founding father" of free/open software dual licensing among FOSS wonks is L. Peter Deutsch, of Ghostscript fame. His companies ran a number of business models in their early days, dual licensing among them. The canonical "popularizer" is probably MySQL AB, followed by Trolltech/Qt. These days, Open Core is riding high. Dual licensing also had its day, and may again.
The more general pattern of "free under these public terms, else pay us" for software goes back far further. Mosaic and Navigator were early Web-enabled examples. Before that, some "shareware" traded on physical media was feature-complete and unlocked, but license-limited, on the honor system.
Outside of software, in other media covered by copyright, the model is old as the hills, and far older than the Free Software movement. Especially with noncommercial terms for free use.
I know Qt changed ownership (including being bought by Nokia). Qt Group for sure did not pioneer it as they didn't exist in the 90s. Not the same company as TrollTech.
Were they the first with dual licensing FOSS and proprietary though?
A disadvantage is that it goes against collaboration of people who don't profit from the proprietary version. They need to dual license their contributions by assigning their copyright to the organization (as FSF also requires). How many people refuse to collaborate as a result of this?