GoogleFrog,
I was thinking somewhat along these lines. The itch.io launcher needs access to the internet, because it has no way of knowing which engine and chobby to start. But the steam launcher does. Theoretically (since I don't know the implementation details), it should then be possible to use the itch.io launcher to get updates and the steam launcher to launch the game when you don't have access to the internet. But the steam launcher might depend on the steam API (I don't know), so that is handled by SmartSteamEmu.
But really, the documentation is somewhat scarce, and the launcher developer didn't make any in depths explanations on the topic when commenting (on this forum or elsewhere, I don't remember). For example, it's not clear what exactly the itch.io launcher does, and how it differs from the steam launcher. So for example it's hard to tell why you can't e.g. launch the game and chobby manually.