They're probably all connected through Doctor Who I suppose, with its lead character's ability to travel anywhere in his TARDIS.
During 9th & 10th Doctor stories, Star Trek is a television show referenced by people as we would, because of its memorable pop culture status... and in a comic-book, presumably connected to the 11th Doctor, he and his companions will suddenly be rub shoulders with the TNG crew and the Borg.
In 1993, the Doctor flipped back and forth between different incarnations while trapped in Albert Square, with its residents getting old and younger too. That's the location of a fictious British soap opera, generally considered as such in-universe when the show was eventually revived in 2005.
No doubt Sherlock Holmes has been both the literary creation of Arthur Conan Doyle and a real person at various points in its 50 year history too.