Depends on whether there are any changes to the PR if it merges. Currently it would not be enabled by default, so you wouldn’t see any changes and have to switch to using the new option manually.
If you’re using NixOS stable, you won’t have to consider this at all until the next release (November/December), at which point the release notes should tell you if the PR merged and whether the setting is enabled by default. Even if that’s missed, you’ll just see the messages twice, or nix will tell you there’s a conflict if the activation script names overlap.