I have uploaded another small update (3.1.5). The emulator:

• Camera key can be used in the control scheme.
• Pause menu has a button to invoke the task switcher.

And the GUI:

• Added support for camera focus key in keys configuration.

With a volume button assigned to L and the camera button to R, it feels almost like holding a real GBA.

Unfortunately, this scheme is not usable with camkeyd. But to make up for it, I have added a button in the pause menu, which makes it possible to activate the task switcher without sliding out the keyboard.

Custom commands in the GUI are also pretty useful: with "sudo stop camkeyd" in "before" field and "sudo start camkeyd" in "after" I can automatically gain furious button mashing capabilities when the emulator is running and get fast window switching back after it is closed.