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.
Yes, SILE is an acronym but to be perfectly honest I can't remember what for. I promise it was good. "Simon's Improved Layout Engine" is a backronym.
But if TeX does what you want, please use TeX. I don't see much point in "convincing" people who are happily using a piece of software which fits their needs to switch to something else which may not. Do whatever works. TeX has CTAN which is the product of many years of work, and it'll be a long time before SILE can even "compete" on level terms with that. But I'm not interested in competing; I'm interested in being the best in a particular niche. If that happens to be useful for others, then great.
This isn't designed for people who don't know TeX, although of course they're welcome to use it. It was designed to solve particular typesetting problems (which came up primarily in the context of typesetting Bibles, parallel texts, and especially in non-Latin alphabets) which were difficult to achieve in TeX.
LuaTeX gives you hooks into the TeX system to customise certain aspects of the program's behaviour. But you can't customise the core TeX algorithms. Because the whole of SILE is written in Lua, you can replace any of the core components.
For instance, grid typesetting is a known difficult problem in TeX and its derivatives, but it's very easy in SILE because you just change the way vboxes are added to the vertical list; it's about 30 lines of code.
The frames support is pretty compelling for me as well, and will be even more so as soon as balanced frames are finished.
It doesn't, yet; TeX is very good at that, so if that's a need you have, stick with TeX. I'm not trying to corner the whole typesetting market!
However, it shouldn't be difficult (especially now that MathJax is in Javascript, a language not a million miles away from Lua) to add support for maths typesetting. Patches welcome!