The New Zealand Geographic board has unanimously ruled that "Whanganui" should be spelled with an "h". And their reasoning is pretty compelling:
Other information the Board considered included evidence of the use of the ‘h’ in early historical records, and the fact that the issue of spelling was one that began from the 1840s. Views of the Human Rights Commission and the Te Taura Whiri i te Reo Māori (Māori Language Commission) were also noted.History wins over redneckery for once, huzzah!“In the end we could not overlook the fact that Wanganui is not correctly spelt and it is a Māori name that is of significant cultural importance,” Dr Grant said.
“Historical evidence has shown that early settlers clearly intended the name of the city to be derived from the Māori name for the river, and consistent modern usage of the language showed the spelling should be Whanganui, not Wanganui.”
The decision will now go to the Minister of Land Information (yes, we have one; he doesn't get out much) for final approval. If accepted, then local authorities and government departments will be required to use the new name in official publications. As for the general public, no-one is going to be stuck in jail for using the old spelling; they'll just increasingly look like rednecks and relics, like those who cling to "Egmont" rather than "Taranaki", or "Rhodesia" instead of "Zimbabwe".