I just checked and space bar does work to start/stop the stream with the latest firmware.
Also using a wireless keyboard here. I prefer the $20 Rii mini i8+, just make sure you get the version with the dongle and not the bluetooth version, works perfectly with Webcaster.
BTW, you can press “m” to turn the USB camera on/off.
If you press “6” on the keyboard you will go to a view with just one camera, the other number buttons reveal the rest of the layouts. Pressing the “tab” button switches between the cameras.