After updating the Ikea gateway to the latest firmware 1.15.55, the openhab binding does find the switch. But it only shows channels for the battery status.
In the code at github, I looked into the tradfri README.md which says that it only supports Battery Level and Battery Low for this device (type 0x0820).
I also planned to buy Tradfri motion sensors. (BTW the README.md names it “Occupancy Sensor” and “motion sensor”, I think the naming should be consistent). For this device too, the only supported channels are about the battery.
So - is it really not possible to get events from the switch and from the motion sensor?