Earlier quoted context omitted.
> it's not even limited to now-obsolete hardware That's not correct, it is limited. The primary reason being GPU drivers, Vista switched to hardware compositor, as a side effect they reworked kernel API of GPU drivers. I don't think Intel, NVidia or AMD ship drivers for WinXP x64, or Server 2003, for their current generations of products. To lesser extent, same applies to the rest of the hardware: I don't expect it's…
Isn't there a fallback driver that almost all graphics cards support? It seems like if anyone wrote a single implementation of that it would work.
The driver is called “basic display adapter” or something like that. Modern Windows is barely usable without 3D GPU acceleration. Too many pixels to render and doing that on CPU is too slow, especially so on laptops. Vast majority of modern software, web browsers included, normally use a 3D GPU to render. And since Vista, windows desktop compositor, dwm.exe, uses a 3D GPU to compose windows into desktop.
Old Win32 apps working on XP will be OK, though. WinXP shell didn’t require nor use a 3D GPU, and very few apps of the era were using GPUs. Unless you have too many pixels in the display, or the app in question renders 3D graphics of any sort, the performance probably gonna be adequate.