This is sort of a user experience and graphics design question, but it seemed better as user experience.
To start, good text has good typesetting. This sometimes means per-letter spacing adjustments, hyphenation at the end of a line, etc. From my understanding, in traditional typesetting environments, the typesetter manually says exactly where each of these adjustments are made. When computers came out, they tried to solve the problem of automatically doing this (such as with TeX). But in the end you still end up having to manually specify things like the hyphenation patterns, and specific spacing adjustments that might make the document look better.
This won't work in an environment like the browser where you have variable sized screens. This is why there are ideas like breakpoints, so you only have to design your layout for a few variations of screens. For a document that would mean you would specify the per-character, per-word, per-line, etc. spacing and adjustments, per breakpoint. Which already that is a lot.
Then there is the problem where, even between two breakpoints, you could have a fluid-width region of text. So essentially breakpoints doesn't work that well for text, unless you are okay with having horizontal scrollbars on your website in different situations.
It seems possible to have fully automatic solutions to laying out the text in such fluid and variably-sized screens, but it doesn't seem (at least currently) to be possible to manually specify them without it being an impractical task.
So the question is, how the typography layout should be specified. You aren't going to be able to practically say "the space between these two characters should be x", for every word/line/screen variation, that would be too much. It seems you should be able to define some sort of constraints beyond any sort of automatic system in place. But the question is how that can be done efficiently and effectively, without having the user/designer have to think about every possible screen size and variation of the text. That is, how to go about making the text look good on the various screen sizes without it being an impractically complicated task.
This is more a user experience problem in how to specify the typography.