If your open source project is significant enough that a company would license it, yes, dual licensing GPL and closed source is a good business model. The succe

If your open source project is significant enough that a company would license it, yes, dual licensing GPL and closed source is a good business model. The success of QT was based on this business model. This however means, you cannot accept contributions by the communite to the code basis without a licensing agreement with every single contributor. For most projects, it is the goal to share the code and get back contributions by the user community. That includes any company using the code. But for that, the license needs to be permissive enough for commercial usage.