smalltorch No, it shouldn't be a system service. It doesn't need privileged functionality to work. I cannot speak for the GrapheneOS project, but I am certain that they will not include this.
User applications are tamper resistant, and installing it as a user application does not increase attack surface. The latter cannot be said about making it a system app.
Make an app, post a GitHub release, and post your APK certificate hash to an independent, trustworthy source. Or better yet, contact the Accrescent maintainers to get it there.