For simplicity's sake, let's say this is what our tree structure looks like:
We would like to manage our 'spare laces' products in just one subcategory, and have a menu item linking to that same content in the 'men' section , and in the 'women' section.
What would be the cleanest way to achieve this? Is there some way to add a 'symlink' in the subcategories, that shows a subcategory item that you can point to whatever URL you want?
All the products you'll add to those categories will be selected by hand or you can define a criteria (or attribute) where all the products with that attribute should be into that category?
The products in this category will be selected by hand, it would be nearly impossible to filter them out based on attribute. In fact, we already have a quite large amount of products in the category.
In that case, I guess, the best approach should be an observer for the admin.
The observer could listen only for that category and when products are changed you should check both lists and pair the lists.
If not a cronjob could work (but you'll get a small window of time when some products will be missing in one of those categories).
(my 2 cents)