1.0.0 will be reached when, given an appropriate style sheet, SILE can perform unsupervised typesetting of an arbitrary USX file (XML-based Bible translation document) to publication standard.
So, I'm really sorry about the examples. There are two issues here: first, I'm not good at coming up with compelling examples. Second, I'm not very good at keeping the examples on the web site up to date with the current progress of the code. In fact, I haven't regenerated those examples, like, ever. Try the PDF examples in the repository as they should be better; but at the same time we should still auto-regenerate them periodically, maybe on release. (And convert them for the web site.) Really sorry about this.
Of the issues you've mentioned: I now justify the columns; the overfull box is gone as I tightened up the linebreak tolerance on narrow columns; kerning most definitely happens automatically if the font provides kerning pairs; grid layout now works better.
Any other issues, please file bug reports and I'll fix them!
It depends on what world you operate in. For science-related work, then yes, I agree it's a dealbreaker. SILE is currently focused towards humanities publishing where not having math support is not really that big a deal. But I would like to see it added, and have been looking into how hard it would be to get MathJAX support.