So long as they are able to insure that the fallen fruit doesn't become a slip and fall hazard this sounds like a wonderful project.

It seems odd that "her efforts were repeatedly thwarted by [...] San Francisco nonprofit Friends of the Urban Forest", as that sounds like the type of organization that would support such an effort.

My impression, although I don't live there, is that San Francisco has a fair number of homeless people. Surely they might be recruited to pick and dispose of ripe fruit before it becomes a hazard? In those locales that require refundable container deposits for the purchase of beverages, the homeless contribute a great deal to the fact that such refuse is absent from most streets. A piece of ripe fruit is surely worth more than 5¢.

In my neighborhood, the homeless root through everyones' garbage and recycling bins in search of redeemable cans. In the process they scatter trash everywhere. It more than counteracts any litter they might also pick up.

Except municipal trees use heavy doses of systemic insecticide at the roots to avoid having to spray them. I wouldn't eat the fruit from a branch grafted onto a municipal tree.

http://www.nyis.info/?action=eab_municipal_tree_management

http://citybugs.tamu.edu/factsheets/landscape/sapfeed/ent-60...

These are interesting links, but they have to do with treating individual ornamental ash trees that are infested with a particular insect. Fruit can only be grafted onto the same species (or a very closely related one) so this has no particular relevance. Information about standard treatments for ornamental plums or crabapples would be relevant, though.