The wifi extender would be the most useful except for the fact that it needs power, and most people turn their lights off when they aren't in the room.
Of course you could also replace the power switch with one that communicates wirelessly with the device and doesn't really turn the power off... But now you can't safely change the bulb... So a replacement switch that does a 'soft' and a 'hard' off, just don't get them confused and touch the pins whilst replacing the £150 bulb when it's blown...
Bluetooth as an audio option is a terrible solution in a house IMO, not to mention the power problem again and the limited size that means quality will be poor.
What was the last one, IP camera, meh... Maybe, if that's on wifi and not bluetooth, although personally I like my cameras to point out of the house, not into it. Presumably this function will mostly be used by pervs to spy on guests in the spare room.