(Person that actually uses sumercé here.)

The article is reading way too much into it, and it forgets a very important piece of information: The origin of usted is "vuestra merced". Spanish had T-V distinction, like most romance languages, but usted superceded vos as the formal 2nd person pronoun.

sumercé is a word that had the same process, just starting from "su merced" instead, since in Colombia —like in all other latin american countries— vosotros is not used.

That's it.