The description is available in Confluence.
It is possible to create links between tables,
It is possible to remove the renderer only (the drop-down),
It is possible to entirely remove the foreign key.
In the first release, we won't implement:
The ability to choose whether the user can create new values in a drop-down. He'll have to go and add the value in the target table.
The ability to change the ON DELETE SET NULL default. The other values could have been CASCADE or DO NOTHING.
The ability for the Join wizard to auto-suggest tables with a relationship.