While it may be possible to develop such Open Source drivers for Windows on a technical level, economic and social realities mean that such a project would not get traction.
First, let's think about why there are Open Source graphics drivers for Linux.
Part of that is the culture, with a sub-group of Linux developers and users insisting on Software Freedom, even if this means avoiding more convenient and more feature-rich proprietary software.
More importantly, the Linux Kernel does not offer a stable interface for drivers. If drivers are upstreamed into the Linux Kernel, they will be maintained there, reducing the needed development effort. GPL-compatible Open Source drivers also get full access to all Kernel functionality. In contrast, externally maintained drivers might break with every Kernel update, and proprietary drivers only get access to a small subset of Kernel functionality.
Having graphics drivers included in the Linux Kernel is a competitive advantage for some companies (e.g. Intel, AMD). For customers of that hardware, “it just works”. Thus, their official driver is the Open Source driver. In contrast, customers of Nvidia hardware have to make do with the limited third party Open Source Noveau driver, or have to download and install the official proprietary Nvidia driver, which is sometimes less stable. It could be that Nvidia believes that their products are so attractive on their own (e.g. due to CUDA support) that Linux customers will jump through extra hoops to use them.
On Windows, all of this is different.
- Windows users tend to consider Software Freedom less important.
- Windows offers more stable interfaces for drivers, making it feasible to maintain third party proprietary drivers that remain compatible with a wide range of Windows versions.
- There is no competitive advantage to be had for graphics card manufacturers to Open Source their Windows drivers.
So given that satisfactory proprietary graphics drivers for Windows exist, and that Windows users generally don't prioritize Software Freedom, it would be very difficult for an Open Source Windows graphics driver project to attract users, let alone more developers. Note that the Open Source Linux drivers for Intel and AMD chips are developed mainly by Intel and AMD themselves. For Windows drivers, you'd be competing against the Intel/AMD/Nvidia teams that are better funded and have better knowledge of the system.