So the clarification seems to be:

Replace "There are some works, primarily historically important photographs and significant modern artworks, that we can not realistically expect to be released under a free content license, but that are hard to discuss in an educational context without including the media itself."

by "There are pictures that are very useful to illustrate articles and for which we cannot realistically expect to get a free alternative. These include historically important photographs and significant modern artworks, as well as pictures of objects and activities out of bounds for people able to take free pictures."

Or did I misunderstand?

I really cannot understand a "fair use" allowance that would include "modern art" but not activities such as seeing the inside of a space craft, or being inside a combat unit, for which access is inherently restricted.

After seeing all these I really wonder if we haven't been misthinking our approach to ESA images.

Please expand. I'm interested in hearing your opinion, since I actually met ESA and CNES about the issue and you did not.

(One thing is, for many ESA images, we don't even quite know whether they're copyrighted and by whom. But that's a bit complex to explain.)