I am not very clear what do you mean by "Editable Experience Fragment where users can select a pre-configured collection of components then be free to edit specified areas.".
Experience Fragment can have another experience fragment/CF in it. If you start with blank template and use earlier created XF or CF would that not solve your problem?
And for pre-configures collection on the page you can always use Editable template, there is an initial content options in it and you so use structure with policy control to configure components to be used.