Shared universe with other franchises

[Christopher]

You're right, my brain somehow juxtaposed Colombo with Diagnosis: Murder

Ah, I see. According to Wikipedia, "George Takei, Walter Koenig, Majel Barrett, Wil Wheaton, and Grace Lee Whitney (all from Star Trek or Star Trek: The Next Generation), as well as Bill Mumy (from Lost in Space), were guest stars in "Alienated!" one sixth season episode, which involved an apparent extraterrestrial life alien abduction and coverup." I think I may have drifted away from the show by then, though I could've seen the episode and just forgotten.

TAS had it's rec room, and the latest SNW trailer has a TNG-style holodeck so ... retcons be retconning.

Well, TAS isn't TOS, and the rec room was only shown to be capable of simulating environments, not people. The "holodeck episode" as a narrative trope was an invention of TNG. The closest thing TOS had was "Shore Leave."

As for the SNW trailer, we see something that looks like a holodeck, but we don't know the context yet, and things are not always as they seem. As Sherlock Holmes liked to say, it is a capital mistake to theorize in advance of the facts.

 

[F. King Daniel]

That's aside from my original crossover point, which they could well execute if they wanted to.

 

[Cicero]

Detective Comics #572 (Mar. 1987), the 50th Anniversary issue. Batman and Robin teamed up with the Elongated Man and Slam Bradley to solve a lost case of Sherlock Holmes.

Although DC Comics did have some Sherlock Holmes connections in the 1970s. Denny O'Neil and E.R. Cruz did a Sherlock Holmes one shot that adapted "The Final Problem" and "The Empty House," and there was a 1976 issue of The Joker where the Clown Prince of Crime went up against Clive Sigerson, an actor who thought he was Sherlock Holmes.

BTW, Mike W. Barr, the writer of Detective #572, is in dire straits right now due to medical and financial difficulties. His GoFundMe can be found here. Please contribute if you can.

There was also a Power Records adventure with a short accompanying comic (later re-released on cassette):

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[JonnyQuest037]

There was also a Power Records adventure with a short accompanying comic (later re-released on cassette):

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Yep, I had that as a kid. Although there it was the ghost of Sherlock Holmes.

 

[Turtletrekker]

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[JonnyQuest037]

Likewise, Munch from the “Dick Wolf-iverse” showed up in an episode of The X-Files — but in an episode of Homicide: Life on the Street (I think), Munch referred to The X-Files as a TV show people were going home to watch.

Yes, but as the X-Files episode "Unusual Suspects" aired in 1997, Munch was still a regular on Homicide: Life on the Street, since Law & Order: Special Victims Unit wasn't a thing yet.

And yes, Munch mentions The X-Files in the 3rd season HLOTS episode "Partners" (airdate Jan. 20, 1995) when he, Bayliss, and Lewis are opening the Waterfront Bar after many months of preparation. The night is slow at first, and when they're wondering where all their patrons are, Munch jokes, "It's nine o'clock. They're probably home watching The X-Files." HLOTS and The X-Files both aired on Friday nights, and Munch actor Richard Belzer was a fan of the show. That's why he made a guest appearance a couple of years later.

Incidentally, Munch's X-Files appearance set a record in 1997, as Richard Belzer became the first person to portray the same character on three different television shows in a single week, following the Law & Order/Homicide crossover episodes "Baby, It's You" on November 12th and 14th and "Unusual Suspects" on Sunday the 16th.

(I'm a big fan of Homicide: Life on the Street and I've actually made a timeline for the series & Munch's appearances on other shows, so I know a LOT about this. )