Solar shingles (Tesla roof, GAF) seem like a smart idea -- why do 2 layers of install, shingles and solar panels, instead save on both material and labor by using solar shingles.
It didn't work because the shingles are small, massively increasing the number of parts, connectors, and wiring -- and all the intensive skilled labor that it needs. Labor needs to be skilled as well as increases the number of hours. It also increases failure rates (at install time?) as well as lifecycle maintenance costs from repairs. Standard shingled roof (not the solar) is just an illegal immigrant working for $2/hour with a nail gun, unskilled labor, finishes things super super quick.
The above is a manual summary from this insightful thread: https://news.ycombinator.com/item?id=48166226
Could it work in future? We don't know. I think the fundamental constraint is people's existing belief system on what a roof is supposed to look like and unwillingness to consider that all roofs don't have to look the same. Perhaps its possible to let go of existing shingle design, build massive panels and make it a structural roof along with metal, but it may not have any buyers. And most definitely will not be accepted by any HOA. Most of the US in in a HOA regime. Any tiniest variation from the rigid HOA rules and regulations (slightly different shade) will require an entire roof rebuild. The constraint is not technological, but human beliefs (about what a roof should look like) and existing rigid structures on how we organized our society.