It strikes me that I treat the result of git-rerere as a ridiculously weak version of this. I'll occasionally carry an unwanted integration branch simply to handle changes that could be managed correctly if there was a better way to express relationships in my tools. Having the functionality baked in to the graph with the associated strictness, and available across clone boundaries would be great.
¹ https://www.cs.tufts.edu/~nr/cs257/archive/david-roundy/Theo...