>>tkgall+(OP)
I started using emdashes in my academic career, after my advisor pointed me to the subtle differences. And since then, I like and use emdash a lot. In Latex, it is easily produced, just keep the spacing rules in mind. The Punctuation Guide is a nice reference on it https://www.thepunctuationguide.com/
>>astahl+1d
There are actually four different "dashes" in La/TeX. The hyphen (-), en-dash (--) which is used for numeric rangen like 1--2, the em-dash (---) for punctuation, and the minus sign ($-$). Knuth talks about them in the TeXbook which is good fun.
>>pxc+Zf
Not in ASCII. My definition of plain text is roughly "the characters I have on my keyboard". Unicode is like a superset of all possible plain texts. Useful, but I really don't like my own files containing characters I can't (easily) type. If I regularly typed in another language I would acquire a keyboard for that language. I'm not even convinced typographical symbols like various dash types even belong in Unicode at all to be honest. It seems like you have to draw a very arbitrary line somewhere.
>>Symbio+Mm
It's not too restrictive for me. I rarely need to write foreign place names or words (I'm British). Yeah I use the £ symbol so I'm not limiting myself to ASCII, just what is on my keyboard (I have € too). I just don't really consider a file full of characters I can't type to be "plain text" just because it's UTF-8, that's all.