There is a need for a kind of 5-20 page intro ("user guide"), a 50-100 page guide ("programmers guide"?) and then the 300-500 page comprehensive manual ("technical reference"?). The tech-ref would (should?) cover every single hardware component, maybe even discuss the System ROM (like the early Apple2 manuals).
Staples or similar online-print-shops were something like $0.50 a page, for a decently thick full color page print. It's really over $1/page, but for a small booklet you can get about 2 pages per full printed page (and that price is including "binding" which is just staples, but it's still a time-saving convenience). So my own little user guide was around $10 with tax and shipping. Its content has mostly held up for the past year (I'd do a few revisions, like mentioning more about BASLOAD and some of the newer "wedge" DOS short-cuts). It was Microsoft Publisher, about as WYSIWYG as you can get. I didn't mind sharing the PUB file, but at the time I didn't understand large-file uploads to github, and the file was something like over 200MB (hi-rez embeded images and such). Now I understand that better and should look back into getting github to host that.
That intro guide is here:
https://github.com/voidstar78/X16_MANUA ... T_REV9.pdf
I'm assuming folks without a github account can access that; if not, then I can see how distribution of any doc will be challenging. But as a compromise, a HTML equivalent is here:
https://voidstar.blog/voidstars-commander-x16-notes/
Near the last page of the manual is some reference tables, sort of in the fashion of those mid-1980s manuals. And in the last half is some starter programming examples. To me, just a few *working* examples is enough to show what the system can do, then it's up to the individual to have the curiosity to go line by and line and better understand how/why things are working from there. But true, a bit more comments and guided commentary of those examples could help clarify things (for those with no background on these kinds of systems).
At the time I didn't cover BASLOAD because it wasn't yet officially part of the ROM. Many people won't really appreciate BASLOAD if they don't already know a bit about BASIC first. There are also notable differences between GW-BASIC, or any "Extended Color BASIC" (which relates to the "who is this for" question - those that never experienced BASIC at all, vs those somewhat familiar with a different dialect of BASIC)
Involving the 65c816 is a messy can-of-worms. While I have an '816 for each of my X16's for compatibility testing, I'm just ignoring it for now since I don't ever plan on writing any '816 specific code. Maybe it could be covered in an Appendix of some kind of "Advanced Guide".