This doesn't apply to GrapheneOS.

This doesn't impact graphene at all

Yes, those are all reasons why Google is a despicable company and how GrapheneOS is going to be more difficult to use with some apps (most likely banking or other more restrictive apps), will be subject to late official Android patching schedules, and how 3rd party apps will not be as usable on official devices, but that doesn't mean GrapheneOS is just dead because Google is trying to kill all custom ROM support.

The Google Play services are already an issue for most ROMs and will be worsened after this, but many apps have releases within F-droid, Accrescent, or directly hosted via github. I don't see how having that will change after this new requirement is in effect. A lot of GOS users already use free versions of apps anyways, that likely won't be affected by this change at all as I understand it. Official app support from Google hosted APKs will be impacted. Most of these apps have workarounds like free open source alternatives or just using the website instead of an app. But some apps won't and that might be a dealbreaker for some people.

From how I understand it, this is a splintering between free software and proprietary software but not a death knell.

GrapheneOS will have to start accepting using microg in place of the Play Services.