The idea of "Reformed Egyptian" in the Book of Mormon is something that critics have lampooned and rejected out of hand from the earliest years of the Church. However, the evolution of Japanese as a written language is a fascinating example of something similar. It easily can be classified as "Reformed Chinese".Without going into long and academic details, what is most interesting to me is that spoken Chinese and spoken Japanese are as different from each other as they are from English. They literally did not originate from the same root language. Also, while many of the modern Japanese characters that originated from the Chinese are still identical to the original, many of them have been simplified so much over the centuries that many Chinese wouldn't recognize them anymore in isolation, out of written context. When you add the two alphabetic systems in Japanese that do not exist in Chinese (one of which designates conjugation forms, articles, punctuation, etc. and the other of which spells foreign words), you end up with something very similar to what I envision with Reformed Egyptian.
To me, Reformed Egyptian simply isn't a legitimate reason to dismiss the Book of Mormon. If anything, the example of Japanese (of which details Joseph Smith was unaware) actually makes references to "Reformed Egyptian" a strength of the book.