Long chilling of brioche dough?
The effect of long retardation of brioche dough is going to be driven by the same basic processes as in any bread dough:


Slowed but longer yeast activity, producing more of the flavorful byproducts (lactic and acetic acids) which give bread the pleasant, yeasty flavor.
Gluten development through autolysation, as the glutinan and gliadin react in the presence of water, forming bonds that create the gluten network.


All of these processes will be modified by the extreme levels of enrichment, so there will be less gluten development and less yeast activity than in a leaner dough.  I suspect (but do not have a reference to document) that that the enrichment will place a ceiling on the absolute amount of gluten development possible, as the gluten sheets will not able to grow as long and strong as they otherwise would, being physically interrupted by the lipids.