The only chance I see would be for Pike to "inject" an emulation layer within boot.efi that will automatically translate all SSE 4.1 microcode calls to the relevant instructions that the older processors can understand. If that were achievable, it wouldn't be the end of the matter, since performance issues might be relevant. In other words, would such emulated operations be fast enough to justify running macOS Sierra on such obsolete and increasingly slower hardware?
You're right ... if so it would not make any sense