> I think it comes down to whether the complexity of TeX/LaTeX is essential or accidental.
I tend to agree with this, but I do think quite a bit of the complexity in LaTeX is accidental. For instance, the existence of numerous packages for basic typesetting tasks, none of which entirely work with each other, are a clear example of unnecessary complexity. Also, as a macro-expansion language, the nature of TeX itself makes some things more difficult than they need to be — consider basic arithmetic, to take just one example.
Furthermore, I’ll note that age really is a big factor here: there are many things we want to do today in modern, computer-based typesetting which were much less important back when TeX was invented. For instance, in a recent presentation I wanted to make two images transparent and overlay them; I had to drag in TikZ (quite a bulky package!) to do so much as modify their opacity. Similar examples are numerous, ranging from hyperlinks to vector graphics to comments to animations.
Of course, typesetting is a complex task, and a typesetting program is never going to be simple. But I feel that fixing the above problems would at least make it somewhat easier than it currently is with LaTeX.
> There has been unsuccessful attempts to remove the accidental complexity, like Lout. It is very hard.
I’ve never used Lout, or even heard of it before now; could you expand on where it ran into problems?