API: read_csv parsing of quoted "NA" value as NaN
From https://github.com/pandas-dev/pandas/issues/10647#issuecomment-123715600

In context of discussion on the default parsing of 'NA' in a csv file as NaN, I don't think we can change the default of parsing `NA`, but we *may consider* parsing of `"NA"` as a string instead of NaN:

> Another change that we would maybe be more likely to consider, is the parsing of quoted values of NA (so only changing "NA" not be converted automatically, but leaving NA and alike converted to NaN as it is now).
Personally, I would even this consider as a bug that it treats "NA" and NA the same, as I would expect that quoted values should be left untouched. But I don't know how long this behaviour has been this way.

Although I am not sure how invasive such a change would be, and difficult to assess, so maybe this is not worth risking many breakages?