if you're writing with the intention of publishing in plain text, doesn't *everybody* fully justify via word choice?! why wouldn’t you; it’s the one medium where you have exact control over line breaking and text flow and it’s not like it’s any different from LaTeX telling you to rewrite your line because it has too much badness
before you consider this an impossible task remember the average english word is four letters and there are a number of one, two, and three letter words, many of which can be optionally included or discarded at the author’s choice
it’s really not that difficult
it’s even LESS difficult if you allow hyphenating long words in reasonable positions and have a sizeable line length to work with
kids these days necc etaoin shrd
kids these days never had to set
text in hot type, i swear to god
you can always add more commas