Now I must admit to being a little shocked, but then everything about the Meyerling mystery is one surprise after another and where the truth is could be anyone's guess. In the book "He did not die at Meyerling", the author mentioned meeting with Rudolf and Franz Ferdinand one or more times and spoke highly of Franz, so it's not like he didn't know him. Some people may just be terrible at photo recognition, but still, you'd think there was some editing for a book!
Despite all, this book still seemed plausible for several reasons. It was supposedly written by a son of CP Rudolf, who was very circumspect about giving any information out that might identify himself or his adopted family. He said he wrote the book to set the record straight and to repair the memory and reputation of his father. He was in his late 60s when his book was published in 1937 and he claimed absolutely no interest in reclaiming his heritage.
Interestingly someone named Robert Pachmann first filed for recognition as CP Rudolf's legitimate son in 1937, but from the dates, he would have been about 5 years younger than the author (R) of the above book. Pachmann kept up his fight for recognition for the next ~30 years.
R's side of the story was that after the semi-coup was overturned, CP Rudolf went to his father to deny any intention of replacing him as emperor, but Franz Joseph was angry still and made Rudolf sign a renunciation of succession for himself and all his children and told him he was not fit to be crown prince. So Rudolf decided to fake his death and move to another continent. Rudolf had a close friend who became R's foster father who was only referred to as the doctor, since he was a surgeon and an artist. The plan was through the doctor's contacts to get a body from the morgue resembling Rudolf, and then the doctor would redo the face using wax molds. His work was about done at Meyerling when Maria Vetsera showed up unexpectedly and thought Rudolf had been killed and she then started fighting with some of the guards surrounding the procedure and she was accidentally shot in the torso.
The couple reasons I think there may be some validity to it is the Emperor was beside himself with grief during the funeral, but within a few weeks, he was unusually cheerful. I don't remember where I read that (not the book) but his quickly recovered cheerful mood was a mystery to many close to him, knowing how much he suffered when his son supposedly killed himself.
The other reason is the disappearance of Rudolf's close friends, including John Orth, at about the same time. I also think Bratfisch and Larisch moved to South America at about the same time as Rudolf's "death". Why would all these people suddenly move to the other side of the world when Rudolf died?
Then there's another story where some thought it was Rudolf who showed up in El Salvador in the late 1880's who became the father in ~1898 of an uncle to the wife of Nash, the protaganist in the movie "A Beautiful Mind". This wife came from a prominant family named Larde' in El Salvador. http://www.math.dartmouth.edu/~lamperti/Justo_Armas.html