I'm a big fan of Pro's project-based approach to managing and sharing content and I've found that metadata on maps, scenes, and layouts can be an effective way of sharing notes, process, and uses within a team (or class). One seemingly important gap is the ability to author metadata for the project itself (project title, summary, description, etc - basically the same info that you would be required to fill in for a web map or any other AGO item). I feel like there should be a very easy way to access this info as it will probably evolve as the project evolves.
In my opinion, the most obvious way to achieve this would be a menu item in the main Project tab where users can view/edit the project's title, summary, tags, and comments (among others). This would be similar to the Info menu under the File tab in MS Word, Excel, etc. Having some auto-generated properties about the current project such as date/user created & modified, file size, number of maps, scenes, and layouts, etc.
I'd like to a rider to this idea as well: I'd like the option to display this project title, summary, etc as a splash screen when the project is opened. This would be an awesome way to provide info to users of the project - especially when distributing as a project package.