It would be tricky to develop a mechanism to detect 'ghostwritten' material and especially one that would be accurate. Writing can be a really 'hit or miss' thing because sometimes the words just do not come easily (or eloquently) so variations in the quality of writing are always going to occur but that being said I think it is better to poorly write something yourself than paying someone else to do the writing for you especially on a platform like this where original content is the 'life blood' of the system.
The cases where ghost writing would be okay (in my perspective) is when an author wants to appeal to an audience in a language they do not know well enough to write in so they write a piece in their native language and then have someone write a translation of the article in a different language and include both written pieces in their article. Even in such cases they should assuredly 'give credit where credit is due' but let's face it there are some underlying human tendencies that are going to make that the exception and not the rule.
When I see posts that have images/videos/writing that people obviously copy and pasted from 'the internet' it immediately turns me off to not just that particular article but also to the 'creator' themselves regardless of how good the rest of their content might be. I actually ran into this yesterday where I read an awesome post that was littered with content elements that I had seen elsewhere on the internet and I had an internal debate on whether I should vote on it or not because I asked myself the question: Should I acknowledge the authentic parts of this and ignore the inauthentic parts and furthermore did I (as the reader) actually gain something meaningful from it? In the end I voted on the post because I wanted to encourage them to keep writing. In hindsight I later thought to point out (in the comments of the article) how distasteful I found such inauthentic elements but could not figure out how to word it in a way that would actually help the author and not just discourage them.
I have encountered the above scenario numerous times on here where folks use content elements from the internet (especially memes) in their posts and if said elements are the 'preview' image (or an obvious cut and paste title) I do not even look at the article. The post I referred to previously had a unique title and preview image which lead me to look at it but once I opened it I was like 'Fuck! Look at all this copy and paste garbage.' This sort of thing (using content elements from the internet) is way more obvious to me than the ghost writing that you describe but I think it is a much larger problem than the ghost writing itself but I am also biased because I am not a curator.
Perhaps a mechanism to flag potential posts as ghost written (that do not credit the author) would be helpful but as with all flagging mechanisms (aside from obvious plagiarism and spam) it is a slippery slope.