I agree! It would have to be a very high ratio of caregivers to kids. Imagine if some of the adult caregivers were themselves on the spectrum? It could be therapeutic for everyone. My idea is to show that even with the cost of a garden and high caregiver ratio, a program like this could save money because of reduced use of hospitals and increased employability.
The visually isolated areas idea that I have sounds similar to what you are saying. It would be cool if people could examine the gardens and design one for themself.
I think it would be a very big mistake NOT to have adult caregivers on the spectrum. There's too much details that the neurotypical people can't really understand even though they are trying. I am currently working on the same ideas as yours and in my concept there is even more autistic caregivers than neurotypical social workers (most psychologists really can't get it so I kicked them out until they prove to me that they can make a good job

) I don't know if that kind of program would really save money on a short term, but it would certainely on a long term, because the kids can learn much faster, even social skills, when they are less anxious.
We have to be aware of the fact that this program would not be good for any autistic kids though. Some will never be able to work in a garden. I think insects moving all around is the biggest problem and there is a lot of those in a permaculture garden. I suppose that I have to accept that I can't help everyone, but I was thinking of adding workshops on the site where the kids could learn arts and mechanics. Anyway, in Quebec, you can work in the garden only from May to October, because there is one or two meters of snow on the top of it for half of the year. And I thought that adding sculptures, paintings and automata to the garden would be very nice and it could even attract tourists during the weekends. Tourists would be good to get a little bit more money, but what is more important is for the visitors to learn what is autism and what autistic people can do if you treat them well.
And if you have enough space to give a peice of garden to everyone, it would be great. The garden will look strange as everybody will have very different views on how the garden should be organized, but if you have visual barriere between the lots... It will be interesting.