With lat/long, you don't need GPS, a paper map is surprisingly effective -- and, in what is the point here, with a paper map (or GPS), you don't need a link to What Three Words' servers. There isn't a good use case for a mnemonic for lat/long that loses the latter's spatial-relationship information.
Above all, the weird thing about W3W has always been that if you have the device to do the lookup, you have the device to exchange and store long and not particularly memorable strings of numbers...
