In the link to the mail list, part of the reply says:
The wiki engine is moinmoin, which is written in Python. Perhaps you
could ask to moinmoin if they plan to include such feature and, idealy,
work with them to implement it.
So I would not go so far as to say it is intended, however apparently it is
in the "moinmoin" software, and maybe no one knows how to make it
"read only" specifically for VPN, users,..
I don't really know the reason VPN users are not able to view it, seems to me
that is more like a problem with VPN's, and not the wiki it'self.
The one thing that is certain , the OP is not the only one that has had this occur,
But this forum is not really going to do the OP any good on this, what they need
to do is contact the wiki administration, and ask them, https://wiki.debian.org/
Down at the bottom of the "Front" or "home" page, there is some links that
will take you to information on contacting the admins of the wiki.
The admins here on this forum have nothing to do with that, nor the forum members, it is a issue that should be taken up with the wiki administration.
Realizing that if the OP is using a VPN, they may not be able to view the information,.on the wiki front page,..if the OP has the means to link,and browse
it with out using the VPN, that is the easiest solution, immediate, or for the time being.
The OP , and anyone else can send a e-mail to :firstname.lastname@example.org
You do not have to join the mailing list,..if you want to check for responses,
you can view them at the list archives: https://lists.debian.org/debian-www/2017/04/
More : https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=789530