Win9x is not a portable OS. Because of its DOS and Windows heritage, the underpinnings are very much tied to x86 and would be difficult to port to ARM. (Although not as difficult as OS/2, which uses the dreaded ring 1.)

Whereas Windows NT has always been portable. Except that Microsoft has already ported NT to ARM.

Indeed, I realize this. My comment was mainly facetious, I admit. Porting DOS/Win98 would be totally silly anyway unless you needed a blue screen generator. Porting ReactOS would start to make sense, if anyone wanted that - say, there was a desire to run windows programs on modern mobile hardware without licensing fees (rendering farm? Most use cases I can imagine would be better served by Linux anyway). Otherwise... Emulation such has DOSBOX makes the most sense for anyone who desires to run legacy Win32 software.