The Great Migration series of books has no endnotes or footnotes and is the Gold Standard of Genealogical publishing today. I guess, in a way, the references to sources there is what FTM used to call "in-line" source references, ie the source reference is imbedded in the sketch textual information. The source itself is treated in a different section of the book that is, in effect, an appendix for sources, with complete info about the source. A completely different approach to presentation than is "normal".
A unique characteristic about this reference is that it is an alphabetical list of geographically based persons and is not lineage-linked. Now, that is something that FTM could add to its repertoire.
Output is the driver of how info should be inputted into your genealogical database, not the other way around. It's all about the output.