yes, this subject came up years ago. the first time I considered it, I lived in new jersey near a new program, just being developed for different kinds of support dogs(besides seeing-eye).
even then the cost and wait were prohibitive.
since then, i have found that many dogs are very sensitive to the n and c events: something about C coming on (the kind that is stress related, i guess, and not startle reflex)
my little dog gets near me, and when i start to curl up and ride it out, he howls and carries on.
LOL, ok so he's not much help.
if a real support animal could be trained to feel our hand go slack on the harness, or something, it would be a wonderful comfort to know someone was standing by.
maybe he could put himself between us and people who have 60 seconds to mess with us!