The real challenge that the article only touched upon is to get lasers into the same package and keep the costs down. This is still an active area of pursuit in both research and industry--though, there are several promising methods emerging. The $10 cost used in the article is likely closer to the cost of the bare silicon die. Packaging is always the expensive part of optics (doubly so if the lasers are not monolithically or heterogeneously integrated onto the same die). That being said, even with today's technology, integrating a laser chip and a silicon photonics chip into a package is easily south of $1k, which is what they quoted competing technologies costing.
I look forward to seeing these sensors integrated into my self-driving car in 5-10 years.
> Our device is a 0.5 mm x 6 mm silicon photonic chip with steerable transmitting and receiving phased arrays and on-chip germanium photodetectors. The laser itself is not part of these particular chips, but our group and others have demonstrated on-chip lasers that can be integrated in the future.
 (PDF): http://www.rle.mit.edu/pmg/documents/OpticsExpress2014Bradle...
Even at 2 meter range with centimeter resolution, these devices would be a much better solution to the "local obstacle" problem than ultrasonics today. Mobile platforms moving around in spaces with a lot of miscellaneous obstacles have to either be compliant (or padded) enough to just push through them or slow enough to detect them and move around them.
That's not always true, it depends on the die size. Bigger dies often means lower wafer yield for optical sensors.