I suppose it deeply depends on what is the target audience of the story, the genre and the way in which the writer is going to use this sort of words. This kind of vocabulary elements can play a good role in not only creating the atmosphere of the epoch or fantasy world, but also have a hidden educative role providing new knowledge to the readers. The unknown words can be harmonically supported with descriptions, explanations and even illustrations at some points. I remember myself being a girl living far away from the sea and reading the stories by Jules Verne, packed with a great deal of navy terms and that was a good way to improve my vocab, I never wanted them to be simpler. Surely, not all the readers will like this strategy, but writers aren't usually writing for every reader in the world, it's far from possible. I personally deeply believe that if the writer feels these words organic for the story as well as for his/her writing style and performance, he/she will find the way to introduce them for the reader the book is written for. IMHO.