Serhiy, thanks for reopening this issue.
It seems to be that there are three reasonable choices:
1. Revert to 3.6 behaviour, with the addition of `docstring` attribute.
2. Change the docstring attribute to an AST node, possibly by modifying the grammar.
3. Do nothing.
I would prefer 1, as it requires no changes to 3rd party code and doesn't present an additional obstacle when porting from Python 2.
2 would be acceptable, as it allows tools to easily convert the body back to its 3.6 form (or vice-versa)
3 is a pain as it involves re-tokenizing the file to get the location of the doc-string.