Can subordinate conjunctions in some cases act as coordinate conjunctions?

According to this guy,

50 Subordinating Conjunctions And Why They Matter

the answer is no.

The coordinating conjunctions are the words and, but, for, nor, or, so, and yet.

There are lots of subordinating conjunctions, including 50 listed in the article, and they all belong within a sentence subordinating a dependent clause to an independent clause. A passage like yours (Mark goes to church daily; although, he was busy today.) contains a fragment.

A few of the examples seem strange to me. I guess that there are words (on that list of 50 words) that can be used as subordinating conjunctions or in some other way, so that a string of words beginning with one of the 50, intended as a single independent clause, could be objectionable or not, depending on the sense.

To me, the following sentences sound correct, although they begin in a naughty way.

• Even my mother agrees.
• Now I like swimming.
• Once I built a railroad.
• Why are you angry?

I have trouble imagining why the first two are on the list at all. I guess that in some foreign place they say things like “He left it at home, even he knew he would need it,” or “He will bring it tomorrow, now he knows he will need it,” where right-thinking Americans would say “even though” and “now that.” But even then, I don't see the objection in making "now he knows he will need it" an independent clause.

Maybe the next two examples are on the list to prevent these constructions.

• I will call you tomorrow. Once I have made my decision.
• I figured out. Why you are angry.

There, the periods before “once” and “why” should be changed to commas, and the following words should be in lower-case.