I was wondering if there are possibilities for extensions to add-ons on the marketplace? Such an extension must require the main add-on installed to work.

Are we allowed to add a new package that requires some other package to the marketplace? Some times users see extended needs than the main package, and want to buy some extension.

Both the developers and Concrete5 will profit on such a functionality.

One solution would be to enable extended functionality when user pays for it, but that is not fair towards C5, since that transaction would happen outside the C5 marketplace.