Talk to someone deep in the GIS rabbit hole and you'll get a rant about how bad W3W is: https://cybergibbons.com/security-2/why-what3words-is-not-su...
Von Braun reported that the rocket had six nines probability of success.
https://www.walklakes.co.uk/opus64534.html
The biggest fault (besides being proprietary) is that you must be online in order to use WTW. The times that you might need WTW are ALSO the times you are most likely to be unable to be online.
That doesn't seem to be the case anymore.
It's still not a great system – many included words are ambiguous (e.g. English singular and plural forms are both possible, and an "s" is notoriously difficult to hear over a bad phone line), and it's proprietary, as you already mentioned.
Aviation already uses phonetically pronounceable waypoint names. Typically 5 characters long, for example ALTAM or COLLI for RNAV (GPS) waypoints. Easy to pronounce, easy to spell phonetically if needed, and easy to enter.
The problem is the list of waypoints are independently defined by each country, so duplicates are possible between countries.
Rather than replacing a system that mostly works (and mandating changes to aircraft navigation systems, ATC systems, and human training for marginal benefit)... an easier fix would just be to have ICAO mandate that these waypoints are globally unique.
If only.
For whatever reason, by convention navaids never use a country prefix. Even when it would make sense - the code for San Francisco International Airport is "KSFO", but the identifier for the colocated VOR-DME is just "SFO". (Sometimes this does make a big difference, when navaids are located off site - KCCR vs CCR for Concord Airport vs the off-site Concord VOR-DME, for example.)
It's even worse for NDB navaids, which are often just two letters.
Either way, were stuck with it, because it's baked into aircraft avionics and would be incredibly expensive to change at this point.
"Waypoint Charlie Alpha Dash ALKOG, over."
"This is an old machine, so just ALKOG then, over."