This would probably be unnecessarily expensive.

wcpoon wrote:

What about just one level down? i.e. listing the number of immediate
sub-categories and the number of immediate pages that below to this category.
This prevents circularity, and also the running cost could be amortized as follows:

Each category keeps the two counts as part of its database entry.
When a page/category list this category as its immediate parent, the
corresponding count is incremented.
When a page/category delist this category as its immediate parent, the
corresponding count is decremented.
When this category is listed as a subcategory of its parent, the two counts are
furnished for display.

All the above operations take constant time.

dbw wrote:

I would also like to express my support for such a feature. Just brackets after
the sub category name, which contains the number of objects within that
category, wich I suppose should hold both pages and further subcategories.

FT2.wiki wrote:

append (X/Y)

where X = direct member articles and Y = direct member subcategories?

This bug seems to be much easier now that bug 6943 has been fixed.

If I understand this bug report correctly, this already works on Wikipedia (probably through the CategoryTree extension). If not, please reopen the bug with a description what is still missing.