Over the past couple years, .so has been pitched by Namecheap as a generic short TLD.

Try this: Search Namecheap for a random domain name. Scroll down a bit to see their list of suggestions. .so is always on the list, next to .cc and similar TLDs.

".so" is perhaps a little bit more clever-seeming. "Readme.so" implies "so... what?"

Anyway, the "country-based" TLD system is busted. People register whatever they want. Similarly, it used to be that you could only register a .org if you were a nonprofit or NGO, but those days have long since passed...

Besides, this is sanctioned by the Somali government. It gets them paid. Anguilla makes a ton of money from the .ai TLD.