Re: Given that...
It stopped until the pentium pro came out in the 90s, and has been present ever since. They probably got burnt by the FDIV scandal and wanted a way to work around it.
'user upgraded' is overstating it, 'user installable' is more accurate. Yes there are microcode updates available, but this depends on intel making them available, there is no documentation or ability to construct your own microcode.
If you have a Sandy Bridge CPU (~2011) onwards you'll probably be patched. For anything else you'll probably be out of luck.
Biting the hand that feeds IT
