(Though I’m not convinced that will actually work on modern apple devices, where the led is pixels that run through the compositor — I guess the video driver stack and window managers are also exclaves in this world?)
Once you have that, you can take the idea further: Displaying an indicator that confirms that all your keystrokes are going to an exclave validating your password, for example.
The much-hated touch bar actually enabled just that, for Apple Pay payments, as far as I remember: It could display something like "touch to confirm payment of $x" on its own screen in a way that was impossible to manipulate from macOS – now here's an opportunity to bring that level of security back without requiring a dedicated display or taking away people's beloved function keys.
I would expect that to mean they're not included in screenshots so I'm curious now whether that's true for the iPhone 16.