We have a suggestion from a user of visually expressing the borders of each DRD into the DRG. Something like this: https://karreiro.com/assets/dmn-editor-supports-multiple-diagrams-now-2.png. He also mentioned that would be nice to be able to change the name of a DRD into the DRG canvas (instead of relying only on the Decision Navigator).
DMN 1.3 supports the persistence of this kind of visual group, so I believe this is a great opportunity for us.
So, when we start working on the DROOLS-5651, we can take a look on this JIRA (which is specifically focused on the "borders" or the visual UI element that will represent them.