Re: "Windows NT has historically supported five different platforms "
MIPS is still competing in the embedded space, although they are way behind ARM, and really missed their chance to get ahead of ARM in the transition to 64bit.
MIPS had a 64bit variant *long* before ARM, it's been around since the early 90s and has mature compiler support, as well as hardware available easily and cheaply. ARM64 was only announced in 2011, and took a while to get OS and compiler support.