Tesla is already manufacturing solar shingles, they use tempered glass and are more than three times stronger than standard roofing tiles https://www.tesla.com/solarroof
Look into the labor it takes to install an entire Solar Roof vs installing a new roof plus traditional solar installation. On a dollar for dollar basis, it may look competitive but Tesla is selling their Solar Roof's at a loss.
Tesla is selling their Solar Roof at a loss. Not at a profit. It's labor intensive and they aren't growing at a fast rate because of that hidden expense.
Disclosure: I installed around 200kw of solar panels and did a decent amount of research into Tesla's Solar Roof since it seemed so novel and innovative. The wiring of the Solar Roof is much more complicated than what is publicly understood. Tesla's good at PR because most of the public are superficial in their understanding. Tesla most likely saves a lot of money in the manufacturing process of the solar shingles but they lose money due to their complicated wire installation process. How are those shingles connected on the underside? How are those wires protected from the elements, without affecting the plywood on the roof? Etc. These are simple questions that are often overlooked.
First one that cropped up in search: http://www.reuk.co.uk/wordpress/solar/solar-roof-tiles/
In the UK, mounting solar on top of the tiles is far more common as roofs are rarely replaced.
Currently, even in Cali a solar system ranges at about $4-5 per watt. The cost to redo a roof depends on the size but almost certainly it would be cheaper than the extra $2.65-3.65 watt left over on using a conventional system and less long-term liability to homeowner to replace a roof and do conventional solar.
Commonest UK size for solar is currently 3-4kWp, which is plenty for household independence, and above 5 or 6 rare. Earlier systems were smaller as panels were costly. I think somewhere around 5 is the point an installation is considered commercial rather than domestic making larger even less attractive.
Exorbitant or not it pays based on UK electric prices and feed in tariffs.
No idea of current prices, and Tesla are available here too. The couple of times I've seen solar tiles in situ (like I say, not common here), have been far more like the last photo than the first which stands out.
Why not lay wires across the sub roof first that the panels clip into?
Or another idea is have the panels pass power between themselves to a single output connection point?
Tesla's problem isn't by intention. It's by NEC (and local) code requirement.
For the second question, why not lay it across the sub roof: Water can be very damaging. What insures those wires (over 20-30 years) will not be damaged? For a conventional solar installation the wires are elevated and protected due to the cavity of each panel. Local codes generally require that no wires touch the rooftop, so that prevents the daily ware/tare.
As for the latter idea, I do believe that's Tesla main goal. But to practically do this is an engineering feat that hasn't been solved yet. Can Tesla do it? Sure. But I haven't seen them invest in a solution yet. Heck, Elon is focusing on too much and not fixing this issue. It's okay, he's got bigger fish to fry. But since it's not solved, they will continue to live with this problem.