Similar to the Place Enclosed By tab, could Sources do something along the same lines.
Source A: Periodical Title
Source A1: Volume 1
Source A2: Volume 2
etc.
The sub sources could only be enclosed by 1 superior source record. (Unlike places that can be enclosed by multiple places.) Instead of setting an enclosed by date (ala places) the enclosed by reference would a Reference Type. (Periodical, Multi-Volume Set, etc)
The Source/Citation entry would build its Source Tile from the Source hierarchy from largest to smallest and take the Author and Publication information from the smallest source which holds the citation record.
The Source views would need to have a multi-level Source list as well as the current single layer source list. In the single layer source list, the displayed Tile would need to be the combined hierarchy title. Move the Citation Tree from Sources to Citations ??.
Since the time Nick responded, this is what has been churning around in my head.