I am really curious just how common this is. I know that article existed in 2013, but how many people read it and agreed with it? If you produced a large survey across a broad age range and diverse set of background, how common is this? The fact that I have never come across this before today makes me feel biased towards it being rare. But the very existence of this thread seems to indicate it is relatively common.

I know another person in this thread mentioned a study about short (one word) responses being interpreted differently based on punctuation, or lack thereof. But that doesn't appear to have studied full sentences with or without.

With your example, I am basically blind to the existence of the period. So "I'm fine." vs "I'm fine" are identical in my interpretation. Or at least they were before today. The ellipsis does register as a trailing thought, and I definitely read meaning into that.

To me, a sentence should normally end in a period. However, due to the informality of chat, it is acceptable to leave off in the final sentence of a message. It being there vs not being there has never conveyed a meaning to me. I really would like to know how many things people were meaning, which I missed because of this. Or if people are interpreting my inclusion of standard punctation, with no meaning, as something more.