Something I didn't realize until recently was that the original MIPS version of Windows NT was Big Endian. I'd always heard it said that WinNT was strictly, 100%, absolutely always little endian, and the fact that every CPU that got a port (or was going to get a port) was either little or bi endian confirmed this.

Well, it is true, but Windows did run BE on the original MIPS R3000 platform. And only on the R3K[0]. The CPU architecture flag is still defined on modern Windows as IMAGE_FILE_MACHINE_R3000BE. There's an early test build of Win3.1 + GDI somewhere that runs on this platform.

The actual first release of WinNT 3.1 only supported MIPS R4000 and higher, I think. In little endian mode.

[0] I know the Xbox used a modified NT kernel, I've seen claims that the Xbox 360 also was, which would make it the second NT system to run big endian. Not familiar enough with sources better than wikipedia to trust that it actually was.