Hmmmm, strange that searching for "proofs" in this workgroup doesn't show up that thread. What talk pages did this discussion occur on? Not the page for "Article-specific subpages", which would seem a natural place to have it.
Searching for "proof subpage" finds some, searching for "proofs subpage" finds more, e.g.,:
http://forum.citizendium.org/index.php/topic,2748.0.html http://forum.citizendium.org/index.php/topic,2756.msg22054.html#msg22054 http://forum.citizendium.org/index.php/topic,2764.msg22183.html#msg22183and an older one:
http://forum.citizendium.org/index.php/topic,1085.msg8866.html#msg8866 All I said that was some discussion should be done before such a major structural decision is made, and it was not easy to find such discussion through searching the forums or CZ.
Article-specific subpages are not a "major structural decision", and they are not presented as such.
Even if there had not been discussions I would not feel guilty about introducing it.
(Of course, when I was new here, I waited and observed first.)
On the other hand, I must disagree with your statement that "A proof is a proof -- it is neither 'student level' (even if it is simple) nor 'advanced' (even if it is difficult)." Depending on the "student" and the "course", there are certainly proofs IMHO that are student level. On the other hand, there are proofs that are certainly "high level".
Sure, some proofs are easy, some are involved. But they are proofs. Let the reader decide if he wants to read the proof, and if he understands it.
Many math pages have been using the "advanced" tag to discuss a more sophisticated view of the topic that would probably only be useful to specialists. This is the official description of "advanced" subpages at CZ:subpages.
Many

And a proof is not a "more sophisticated view of the topic", it is a supplement to a discussion.
For instance, the Chinese remainder theorem can be described to an typical university student with standard mathematical preparation, and is useful to non-mathematicians, for instance, to computer scientists. The "advanced" subpage describes the more advanced theorem of the same name that appears only in the context of ring theory and would be useful only to someone with serious mathematical background. Rather than shoving this down the throat of the average reader, the main page simply directs people looking for the more sophisticated viewpoint to the advanced page.
An encyclopedia is intended for all levels of readers. If you want to hide everything from ring theory upwards on Advanced pages,
then most mathematical topics would consist mostly of advanced subpages (similar in other sciences).
Of course, you should try to explain as much as possible as simply as possible, but pages must not be confined
to elementary arithmetic! An encyclopedia is not a textbook for students.
Perhaps an "examples" subpage would be good, but again, it is a major proposal that should be discussed. In my opinion, the "important examples" belong on the main page. Perhaps a more encyclopedic listing of examples is important, and so should be put on an "examples" page. But then one could go overboard, and the question becomes when to draw the line.
I agree, some examples (and some proofs) belong on the main page (even advanced ones):
The main page should give the essential information on the topic.
A reader who does not know the subject should not be distracted by too many details (like too many examples),
on the other hand, some topics have many good (and different) examples, e.g., groups, etc.
I will guess that the reason the types of subpages are strictly controlled is so that we don't go overboard with them, just like we wouldn't want to go overboard with examples.
Only the "official" subpages listed as "unused" by the subpages template are "strictly controlled".
I don't mind if the /Proofs won't get this status (which I find quite unnecessary, by the way).
As an example so extreme as to be ridiculous, one could want there to be a great many examples of solving quadratic equations, but I think most people would think it would be overkill to give 100 examples on an examples page. Well, one should do at least three examples on the main page illustrating the three main types of solution sets. Perhaps more are required, so is putting them on the main page overkill? How many more are required? At what point would they make the main page overly complicated and need their separate "examples" page.
My view: The explicit examples belong on /Tutorials (discriminant <,=,> 0, coefficients real and complex).
On the main page the general situation should be explained.
It seems to me that discussion should result in general guidelines on where to put certain types of proofs, with examples of each guideline, as well as where to put certain types of examples of the topic --- that is, if there seems to be general consensus among the math authors that the added subpages would be worth the extra complication. I see the potential, but I'll believe it more once discussion has happened.
There are already too many discussions that distract from writing pages

Some of these discussions are important. This is not.
Trying to formulate detailed guidelines in advance is the wrong way.
Allow the content to evolve, solve problems when they occur, and write guidelines on the basis of experience - that is the better way.