See the first Topology Manager GUI extension, which lets you map Publication mappings for a Web 8 environment.
When you add a new Site Publication, the system provides default configuration settings that you can use as the basis for your mappings for that Publication. On the one hand, you can see publishing environments that you can map to; on the other hand, you can see any mappings that have already been added to the current Publication previously, and that are not yet related to any environment.
This functionality is planned for a future version of SDL Tridion. Feel free to share feedback here on Tridion Stack Exchange Meta or in a comment for the extension.
Questions about this open source release are welcome on Tridion Stack Exchange.