Serial-Ethernet or Serial-WiFi (or Serial-Bluetooth?) on OS X
Bluetooth may actually be the way to go. There's no standard for Serial-WiFi or Serial-Ethernet adapters (as far as I know), so you'd be at the mercy of the manufacturers who need to provide OS X drivers. On the other hand, most Bluetooth functions come from a set of standardized profiles that don't need specific device drivers. For example, a headset just needs to implement the correct audio profile to be able to work with anything that supports that profile. Bluetooth serial adapters implement the Serial Port Profile, and OS X supports it.

Once you have one of those devices and have it paired, it will show up as a standard serial port device like /dev/cu.bluetooth and /dev/tty.bluetooth, just like a Serial-USB adapter.

If the serial port doesn't get created automaticaly, it can be added manually in the Bluetooth advanced preferences. I also found an example of someone using SPP with a Mac here: 
Using Bluetooth Serial Port on OS X Mountain Lion.