I used to grow & ship landscape plants out of Encinitas - water bill was irresponsibly high & my uncle who was a SoCal nurseryman by trade lost property to wildfire like 3 times before he passed away.
So to intall trees all over LA, you'd need....too much water & too many big deep rootball-sized holes' all over tightly developed land.
If I still worked out there, I would try to sell this author on some vines-on-trellaces or something more environmentally suitable.
The number of enviroment suitable trees' required to scale & make a difference literally don't exist & would take a decade + billions of gallons of water to grow.
Y'all have got to get more creative.
The environmental impact of shade trees is fairly well established science & the proposed solution isn't very attainable.
I don't see the point of this article beyond commentor-fodder online.