The work behind what3words isn't the algorithm. It's the word list used. They have linguistics who check the sounds of words, are they too similar to another word are they rude, etc, etc..
It'd be interesting to apply a Hilbert curve [0] to the Earth with the PGP Word List, with the even/odd list being used for each hemisphere, or used normally as a check. [1]
This is basically what S2 the library I use in https://wherewords.id does, except I don't use the pgp word list because it is too short and would lead to requiring too many words per place.
Well, the majority of the work behind w3w is the marketing.