Historically, Treble predates GKI, created after OEMs disregarded Treble, as Google had the clever idea to leave Treble updates as optional for OEMs.
> Binderized HALs. HALs expressed in HAL interface definition language (HIDL) or Android interface definition language (AIDL). These HALs replace both conventional and legacy HALs used in earlier versions of Android. In a Binderized HAL, the Android framework and HALs communicate with each other using binder inter-process communication (IPC) calls. All devices launching with Android 8.0 or later must support binderized HALs only.
GKI only became a thing in Android 12 to fix Treble adoption issues, as you can also easily check, and GSI was introduced in Android 9, after userspace drivers became a requirement in Android 8 as per link above.
> Binderized HALs. HALs expressed in HAL interface definition language (HIDL) or Android interface definition language (AIDL). These HALs replace both conventional and legacy HALs used in earlier versions of Android. In a Binderized HAL, the Android framework and HALs communicate with each other using binder inter-process communication (IPC) calls. All devices launching with Android 8.0 or later must support binderized HALs only.
https://source.android.com/docs/core/architecture/hal
GKI only became a thing in Android 12 to fix Treble adoption issues, as you can also easily check, and GSI was introduced in Android 9, after userspace drivers became a requirement in Android 8 as per link above.
https://arstechnica.com/gadgets/2017/05/ars-talks-android-go...
https://arstechnica.com/gadgets/2021/11/android-12-the-ars-t...