Pending a response from the Narrative team, here is my sense of the best way forwards.
We should keep the policy of older niches having priority over newer ones, when considering redundancy, EXCEPT when the newer niche has been purchased, and the older one remains unpurchased.
In this situation, this would allow @Emily Barnett's partner to buy the more recent, better named and more clearly described Street Photography niche, and then immediately lodge an appeal for the older, less well defined and redundant Street-style Portrait Photography, to be declared redundant. Because nobody will have bought the older niche, but someone will have bought the newer one, this is the only scenario where the network matches an owner with a niche, gets the best niche it can get, and very little harm is done to any other user. The older niche can be removed before anyone decides to buy it. There isn't really any need to adjust the reputation of the person who suggested the older niche: we can look at their contribution as being judged a positive one at the time, but that needed to eventually become defunct.