It's a cute and clever system. But, it only works when the user has access to a connected device. Sure, it would be possible to publish offline maps containing all three word combinations in an area, but that's hardly as useful or usable as simply publishing maps with the proper coordinates.
Additionally, without a map, delivering mail in those favelas is a PITA. Shacks typically straddle the sides of hills and mountains, so even if you know where you have to be, without a map, you'll have a hard time getting there.
And, if you have a map, you have coordinates, too. Meaning that the three word shorthand becomes much less relevant.
Then, as the three words superimpose a grid, they don't line up with front doors. In favelas and other density populated areas, this will be inconvenient.