Having a real designer...
It should be great to have a designer which supports all mapping (so which allow us to realize TPC, Horizontal Entity Splitting).
It should be great to have a designer that supports partial model views as I did (http://msmvps.com/blogs/matthieu/archive/2009/04/07/edm-designer-new-version.aspx, http://msmvps.com/blogs/matthieu/archive/2009/04/11/edm-designer-new-feature.aspx)
It should be great to be able to see complex types on the designer and not only on Model Browser window as I did (http://msmvps.com/blogs/matthieu/archive/2009/01/07/edm-designer.aspx).
It should be great to not lose all our ssdl changes when we update the model from db.
Closing this as it is specific to EF6 and EF6 designer and we are now only tracking EF Core ideas here. If this is important to you, create an issue at http://github.com/aspnet/entityframework6/issues/new, but keep in mind that moving forward, our team will only fix bugs, implement small improvements and accept community contributions in the EF6 codebase.