To be brief, what I mean by extended has to do with updated Unicode standards. With newer standards they extend the amount of emoji characters that Unicode is able to interpret.
There are different versions of the unicode standard that covers the keyboard characters that interpret a pictograph emoji and other text. Older installed Unicode standards don’t cover the newer library of emojis available.
When I attempted to do this to my own router there were few emojis that the Unicode on connecting devices could interpret. Cellphones were good at showing the emoji characters, literally any you could think of because they have extended more current version of Unicode standard that has hundreds of emojis. Some devices, oddly, like some Windows OS would not show or interpret all the most current emojis.
There were drawbacks to this: some hardware does not interpret the unicode to emoji and you get a string of nonsense for a wifi ssid; like a roku or chromecast. Makes it difficult to connect to your wifi and sometimes impossible depending on the device.
I used to have my SSID set to Tibetan characters, and interestingly, all of my devices could render it fine, but my Android phone refused to connect. Underneath all the UI layers, wpa_supplicant just couldn't. Changing it to Latin script, and the phone worked fine.