The collective "Everyone" represents the real world decentralized internet "hacker collective" known as Anonymous.
Joan starts to write what looks like stories about Sherlock. The majority of the Sherlock Holmes stories were written as if Dr. Watson had written them.
The doll house murder scenes created by Holmes are based on the real "Nutshell Studies of Unexplained Death", which the pioneering criminologist Frances Glessner Lee created as teaching tools in the 1940s. The scenes she created were so detailed that they are still used now as reference and teaching tools.
Sherlock's screen name in the chat rooms is SHolmes221B. This is a reference to 221B Baker Street, which is Sherlock's home in London and in the original book series.
The plot of a group of anonymous hackers maliciously harassing someone was the same as Hackers (1995), also starring Jonny Lee Miller.