It didn't really cause issues for end users, but OS/2 was tied to x86, it actually uses more than two rings and AIUI even Warp 4 still has 16 bit code in variou

It didn't really cause issues for end users, but OS/2 was tied to x86, it actually uses more than two rings and AIUI even Warp 4 still has 16 bit code in various places. One of the reasons for creating NT back when it was "NT OS/2" was as a "Portable OS/2" so that the OS didn't get left behind when one of the upcoming RISC architectures inevitably destroyed x86 (nobody then would expect a clunky CISC like x86 to be on top 30+ years later, or that the nearest challenging RISC would be the chip from the Acorn Archimedes).