Hey!
I actually read that article when designing Fleece! I wish I came across it when making STM but this will prove very useful.
These are all really great ideas, and better hyphenation options have been something on the to-do list for a long time. I think a tag for a zero-width space is a good idea for a built-in feature. (Just like the <br> tag that inserts a \n... could be the lengthy <hlb> like the article suggests...) I believe you might already be able to type "\u200B" but this is very long... I do have an example a script in there somewhere for extending STM with custom tags, so replacing <custom> with "another string" is always doable! I like the article's example of using "^".
I'll take a look at the source and see why those hyphens aren't inserting!