Hi,
I've spent some time today fixing the HelpAuthoring extension, and
together with the Regina's fix (thank you, Regina!), I think it got to a
usable state 
https://wiki.documentfoundation.org/Documentation/Help
describes where to get it, and the basic usage. More detailed user
manual can be found here:
https://wiki.documentfoundation.org/HelpContent
The .xhp's generated by the extension are now nicely formatted, which
means that when you save a .xhp in the help repository, it will likely
be a big diff the first time (due to the changed formatting - strings
should be preserved); but from then on, the changes should be tiny, as
the format will be much better defined.
Also the editing directly in LibreOffice seems to be neat & usable.
There might be rough edges still - but I hope no blocker any more.
In other words - *no excuses* for not writing help any more 
Please do use it, and if you experience trouble, either fix it yourself:
http://cgit.freedesktop.org/libreoffice/contrib/dev-tools/tree/helpauthoring/README
or let me know - the xslt that implements the export filter is trivial.
Would be good to start thinking of a workflow between the developers and
the documentation team - I imagine developers could stub help for things
they are developing, and the documentation team members would then
finalize and de-hackerize that, but ideas how to grow the community of
help authors much appreciated.
[BTW - if you are wondering about the editable wikihelp: no, I'm not
abandoning the idea; but that is a long-term quest, and the help needs
improving _now_.]
All the best,
Kendy