The problem is essentially one of receivers and of power.
A "find my keys" type of beacon needs to be small enough to attach to your keychain and you probably don't want to have to regularly recharge the beacon (you wouldn't lose your keys if they're always in their charger) so that requires either:
- a passive technology without a battery.
- an active technology running of a battery that is extremely power efficient and doesn't require recharging/battery replacement for months or preferably years.
Then you also need a receiver to locate the beacon and in the case of a passive technology you also need a transmitter to power and activate the beacon. The options for receivers/transmitters are either:
- a dedicated and/or proprietary receiver unit, which allows the manufacturer to select optimised frequencies, protocols and technologies, but which means you need to bring out that receiver when you need to find your keys.
- use the smartphone which you already carry as the receiver. That makes the solution a lot cheaper, you only have to buy beacons, but also limits the beacon manufacturer to technologies, frequencies and protocols that are commonly implemented on smartphones.
The advantage of passive beacons is that they're likely to be quite reliable and cheap to manufacture, the expense is in a transmitter/receiver combo that works from a reasonable distance. Most likely you'll need special purpose device to take the role of tranmitter/receiver as smartphones currently only support NFC as a passively powered protocol, near-field communication with a range of a couple of cm.
An example that works over significant distances would be the Recco beacons and receivers marketed for finding people buried by avalanches.
For active beacons the main issue is power consumption. As you listed there are a number of different protocols and solutions that are low powered and energy efficient, but since nobody really seems to want to depend on separate receivers but would rather use a smartphone effectively that means either Bluetooth or WiFi.
As currently phones can only be connected to one WiFi network at the time and when operating as a hotspot can't be connected to another WiFI network at all, that is probably not the most desirable protocol.
With Bluetooth 4 and above on the other hand a large number of devices can be connected simultaneously and that standard also comes with the Bluetooth low energy variant. You also get a reasonable distance from Bluetooth.
So should we stay on BT beacons or can other protocols be more reliable especially for home usage?
In summary: unless you are willing to use a specific receiver to find your beacon Bluetooth Low Energy is the best choice.