Here's the new FAQ.  If I've made any mistakes, or left something out, or some language can be improved, please let me know.  Or if you have the right access, please feel free to change it yourself.

https://inkscape.org/en/learn/faq/?edit_off=true#how-change-display-units-version-092

If anyone is interested in writing a more detailed and technical explanation of all this, in the wiki, we can link to it from the faq.  (Or if there already is one, please give me the address and I'll make the link.

Thank you very much!
brynn

• "It does not correspond to any specific size":
  As a matter of fact it does (right now it's 1/96 inch). The problem is more that this scale - as pointed out by others in the discussion before - can change at the will of the W3C. If they ever decide to change it again we'd neet to scale documents again (but this time it will be possible to do this fully automatic, i.e. should not require the users interaction anymore)
• "It can't be used offline -- for example, you can't print an image in pixels, because the printer doesn't use pixels for a measurement.":
  That sounds as if the printer would stop working if I tried anyway (which obviously is not true). Printing a px-based document works just as well, what users have to be aware of that a "dot" (as in "dots per inch" or dpi of the printer) does not relate to the px in the SVG document which has a fixed scale.

What about dropping the (*) as well as the term "real world units" altogether? I think it's not strictly relevant within the scope of your answer (choosing "px" and "mm" works exactly the same way for users).

Regards,
Eduard