I've worked in typesetting software a long time. And I've seen several OSS projects reach roughly the point this one has before dying. I can recall only one or two that made it significantly past this point. The challenge is not the coding but the domain problems. It's easy to get a core set of features with very basic operations going. But pushing on into the required capabilities for more than markdown-level formatting is very, very difficult. The issues are mirages, b/c they appear easy to explain, but they're extremely difficult to implement.
For example, footnotes. We all understand how footnotes should be placed--right there at the bottom of the page. However, placement become very difficult if you have a long footnote that appears in the before-last-line of the page. Now, if you include the footnote, there's not enough room for the last few lines of regular text, and the footnoted word is bumped to the next page. Figuring out how to get out of this one problem algorithmically involves heavy-duty backtracking work, projections of layout, recalculations, etc. Its difficulty is compounded if other factors enter in. For example, if the text and footnote appear just before a full page image, etc.
Another classic difficulty is widow and orphan control. Knuth's algorithm on this topic alone requires almost 100 pages to explain [Digital Typography, 1999].
And so on. Suffice it to say that Donald Knuth spent 10 years writing TeX, much of which he did full-time, supported by various grants.
Typesetting is a really, really hard problem domain and while the author here expects to add features like equations soon, to those of us in the field, it feels like he doesn't really grok the difficulty of the problem domain.
The odds are small that he can climb the cliff in front of him unless he's willing to work on this full time for a very long time.
Nonetheless, I wish him good luck.