Use custom jack socket with plug detection. Hook the audio pins to Pi jack and the detect pin to GPIO. Make sure the detect pin works against ground (most of them do, but there always is a possibility of some exotic configuration).
You pretty much can't use the Pi jack directly anyway, as doing so would put the power port toward the customer.
Depending on ...
You can listen for ACPI events and act on them. You can use acpid directly or a client called acpi_listen that comes bundled with acpid.
acpi_listen works as following:
jack/headphone HEADPHONE plug
jack/headphone HEADPHONE unplug
Section 3 at the bottom of the installation guide Troubleshooting part:
Couldn't acquire D-Bus name: org.bluealsa
It is not possible to run more than one instance of the BlueALSA
server per D-Bus interface. If one tries to run second instance, it
will fail with the "Couldn't acquire D-Bus name: org.bluealsa" error
message. This message ...
You need to configure Raspberry Pi as an audio streaming server and the Arch Linux as an audio streaming client. In this case, both Raspberry Pi and the Arch Linux have to be joined to a local area network.
By this link, you can do it over TCP to a server running the PulseAudio daemon. Follow procedure up to "Zeroconf (Avahi) publishing".
The subdevices are for multiple audio services usage that would be mixed to input/output.
There are also subdevices that are a part of an input or output
device. There must be at least 1 subdevice. In the context of output
devices, a device having multiple subdevices means the hardware can do
mixing, i.e. it can take multiple streams of PCM and mix ...