No, it's not a common type of story. Such a story with this specific topic is rather niche and might be considered inappropriate or too private for general discussion.
I'm not sure specifically what that particular 'giant black dildo story' is about as the title is rather unclear without more context. It could potentially be a fictional or perhaps a very strange and specific anecdote within a certain community or narrative.
I'm not sure specifically which 'wife dildo story' you are referring to. There could be many fictional or personal accounts with such a title. It might be a made - up story in a certain adult - themed context, but without more details, it's hard to say exactly.
The significance of 'the giant black dildo story' is very much in question. If it is a story that was created to make a statement about sexuality, power, or some other complex concept, then it could have significance within the framework of those discussions. But if it's just a silly or shock - value story, then it may have no significance at all, other than being a strange and somewhat off - putting title.
It can be appropriate in certain creative and consensual adult spaces. For example, in erotica writing where the readers are aware of and interested in sexual - themed stories. However, in mainstream literature or in places where there are moral and ethical boundaries regarding sexual content, it would not be appropriate.