I'm probably out of my depth here, John may have more experience here.
on the HOA scenario here would be my answer
1. No :). Of course there are discounts for security measures, gates, guards etc. that everyone would get but homeowners premiums are derived on so may factors such as insured age, household members, claims history, ROOF AGE, age of the home, scheduled property, pets etc., so if each home is individually owned this would be near impossible. Also, carriers don't want to have a big number($) tied up in one area where if one claim hit it would decimate profits. I do a lot of Condo Associations and I'm having more and more trouble with having companies having to cover such a big property amount in say an acres or 2 of land mass.
2. have no idea
3. not sure about regulatory barriers because there have been plans done through employers or associations where they'll give a specific discount, let's say 5% overall to the employees they can write but that being said those clients typically don't live right next to each other, have the same age/style/value of home and they still have underwriting guidelines they have to go through that can generate rate or every deny the coverage.
That help at all?