Family search has done really great at the memories gallery and their pictures. Basically when I upload a picture from the picture I can tag every person in the picture and I don't have to go to each individual person and tag them but I can do that from the picture. This same concept needs to be done with sources. When I upload a source I should be able to tag everyone in the source from the source, instead of having to go to each individual person from the source box and tagging them I should be able to do it from the source itself.
One potential issue I see with this that is less of a problem of pictures. Is duplicate sources which is more annoying for sources than pictures and memories. However, they should dedicate more resources to making adding sources better like they have done with memories and pictures.