Lllkkk I wish people stopped talking about a situation we literally have no details on OTHER THAN it won't effect modified android systems that aren't even running Google Play Services.
Will there be a developer settings toggle? Will there be just a warning? Will ADB or similar bypass it? Will users just now have to sign their own applications with their own hobbyist key? We don't know, and we won't know until Google gives more info.
A lot of assumptions being made that don't have good justification for it. Reminds me of when the Pixel 10 was being announced and everyone was betting on the bootloader being locked, or that GOS will stop being maintained due to the Android 16 device tree.
tl;dr; It won't effect GOS in any capacity