My wife has just re-inquired and a Guangdong office has suggested an application to renounce her and my son's citizenship. As this was done by phone and as my wife omitted some, to me important, questions, we are contemplating a follow-up.

Your post gives me the impression it's not a difficult task for Chinese folks with Western spouses and mixed offspring to renounce their citizenship, But in contrast, it's very very hard for Western folks with Chinese spouses to obtain Chinese nationality, not that many of us would want to.
Cheers and beers to those policy initiators who obviously appreciate the presence of westerners in their honourable, though not internaqtionally honoured, country!