Why do we pigeon-hole authors, their characters, and their writing styles to a certain, compartmentalized segment of the literary world? ...What would a Holmes novel sound like if Hammett was the author? How about a Spenser novel written by P. D. James? A Perry Mason book written by Michael Chabon? Heck, what if Doyle himself wrote a Continental Op tale?
...[W]hy are experiments like this not the norm in literature? Are we so conditioned to having Holmes and Watson always live in 189- that we don't want them to sound like the pulp heroes of the 1930s? Are we so worried that if Spenser starred in a story that "sounded like" Agatha Christie wrote it that we'd throw the book across the room?
It seems to me the restrictions placed on characters and authors naturally stem from the choices authors must make when creating characters, just as people are shaped by their upbringing and life choices.
Once defined by these choices, characters are expected to stay consistent; the author's fictional world as a whole is expected to stay consistent. People are more allowed to change than characters, but if they do so too often, they're seen as weak of character.
If you separate a character from the world and author that helped shape him, unless the new author painstakingly follows the original, the character will change. Individual readers are left to decide how much the character can change and still be recognized as himself. Some critics said [Jeffery] Deaver's Bond wasn't Bond enough.
Still, I would say experimentation is the norm in literature. Many if not all authors begin by imitating their idols, gradually experimenting with their own innovations. Parker, for example, asked, "What if Philip Marlowe lived in 1970s Boston?" The typical result of such experimentation is not just a new spin on an existing character, but a new character entirely.