Joe, I think your proposal has merit, but for the issue of defining "abandoned". One man's 'abandoned' wire is another man's 'future'.This comes up quite frequently in industrial control wiring, especially when the conduit is maxed out with control wiring per old code..with no regard for derating..and it would be too disruptive and expensive to try to get the wires out. (I know..money isn't what the code is focusing on..unless you see the words, "where practicable")
On the other hand, it certainly would help in situations like I came across in a job recently..they used the old conduit and wires to feed some lights, using black/red/blue, and used brown/orange/yellow for phase colors in the added wiring. This mixed color scheme for the 277V lighting resulted from the effort by the foreman to save some money for the contractor by utilizing the old 'abandoned' wiring!
Then there are the cases like lifting a ceiling tile and finding a 3/4 flex laying on the ceiling with 6 hot wires..with just yellow wirenuts capping them off!
