I watch a lot of public broadcasting. In particular, I'm a fan of Mystery, on PBS, which has been re-branded in the US as Masterpiece Mystery, to connect it to Masterpiece Theater. The program, rather than having a particular mystery all the time, will run short series of other mystery programs and short films, often done for British television, but not always, and then once that season concludes, they'll move on to the next season. They'll run 6 or 12 episodes of "Miss Marple" and then move on to a series of "Inspector Lewis".
Now, there is a history of detective anime. The Detective Conan series is, I believe ongoing, plus there have been other shows before and after that (Detective Academy Q and so on). The thought which came in my head, though, is adaptations of detective novels, from Japan, from the West, and from other countries, and basically doing a short series (even for anime), possibly with longer episodes, with OVA quality animation, on, say, NHK (as from what I understand, it's Japan's equivalent of PBS).
This has kind of been done before with Great Detectives Poirot & Marple, but this would be a little different. The main difference would be by having significantly shorter series, with double-length episodes, you can have a bigger variety of characters, and creators. That way, if the broader audience doesn't like one detective series, you're not stuck with a long-running series, nor do you have to worry about canceling it halfway through and alienating a smaller, vocal fan-base. The viewers who don't like this series can wait literally one month, maybe a month and a half, and a new series starts, with a new detective, a new director, and possibly even a new animation studio. Further, by using this concept, you could more easily get more significant directors to contribute to direct or produce a series, without being tied down for long periods. Similarly, you could get significant voice actors or actresses to agree to play major roles who might otherwise prefer to voice films, or might need to take on a lighter workload for various reasons (age, pregnancy, what have you).
To do this, essentially, three or four mini-series would need to be in production not-quite simultaneously. Each series would be four-to-six episodes long, each episode being about an hour long, with about two episodes per novel, possibly more, depending on the novel and the amount of time the novel would require (short stories could be handled in one episode).
Oh, and why anime? Well, Anime translations into English are more marketable to the west, and quite possibly easier overall than translating novels. Thus, by doing this as an anime, some of the works of Japanese mystery writers which haven't been translated into English could get some western exposure, and thus would expand awareness of the characters outside of Japan. Yeah, I can sometimes be a little selfish like that.
Unfortunately, while I enjoy detective fiction, my knowledge of Japanese detective fiction is minimal. That said, here are my thoughts for the first "series" of series.
Show 1: Kogoro Akechi - From what I understand, this character is, essentially, Japan's first fictitious detective to get a series of novels featuring the character. The character's creator, is a major cultural figure in the same way that Sir Arthur Conan Doyle is highly regarded in the US and Great Britain. However, the detective's own stories have never been adapted to anime. The detective (and/or his descendants) have gone up against Lupin III, he makes minor supporting appearances in Daughter of Forty Faces (which features the daughter of Kogoro's rival), the name of his creator is part of Detective Conan's cover identity, and there have been film adaptations of some of the stories, but no anime. Considering how heavily the Sherlock Holmes stories have been adapted to just about every medium in the west, this slightly surprises.
Show 2: Jane Marple - I haven't seen Great Detectives Poirot & Marple. However, people I know who have seen it, did level complaints about the show, particularly at the introduction of another audience perspective character (Mabel West) as a narrative bridge between the Poirot and Marple cases (as the two detectives have never actually met in Christie's work), plus the introduction of an unnecessary cute animal (her pet duck). That said while the character concept doesn't fit in well with Poirot (particularly the pet duck), it works perfectly with Marple and, as the Miss Marple stories would probably market better for a mixed Shojo/Josei market in Japan, the character would fit in better there. Besides, Christie usually introduced a series of young female audience perspective characters throughout the Marple stories, with often a new character each novel. With the Miss Marple stories, you could basically drop all of those, and have the audience perspective character (it could still be Mabel West, it could be someone new), fit that role in the narrative more-or-less as needed.
Show 3: Lovejoy - My main reason for picking this is to balance the more Josei leaning (but not quite) Jane Marple pick with something a little more Seinen. In this case, Johnathan Gash's knavish antique dealer/forger. The Lovejoy novels have been adapted to the screen once, for a television series with, if I recall correctly, Grenada, starring Ian McShane (who is now better known for his role in Deadwood). However, much of the more risque content, and some of the more violent content is removed from the series. While there are still murders and thefts in the TV series, often deaths are more gruesome in the novels, and Lovejoy is often directly involved in the deaths of the villains. In a particular example, in Gold by Gemini, Lovejoy is checking for clues at an old artillery post on the Isle of Man, when he's trapped there by one of the killer's henchmen. Lovejoy is rescued, but the henchman falls to his death - in the TV version he drowns, in the book the piece of jagged rusted metal the guy lands on, and is impaled on probably contributed more than being face down in the Atlantic. In anime, you could get away with being more accurate to the more violent portions of the story. Further, Lovejoy's frequent discussions directly to the reader in the book (which the British TV series preserved) could preclude the need of an audience perspective character. Failing that, though, Lovejoy often takes on apprentices (who often become accomplices to, say, forgery) because he's perpetually broke.
Show 4: Kosuke Kindaichi - Yes, the fictitious grandson of the character, Hajime Kindaichi got his own anime after a manga series, and the original character got some big-screen adaptations of his adventures, but he hasn't gotten an anime either, which makes him, in my book, very elgible for his own series.
Well, those are my thoughts for this concept. My apologies if this is worded kind of clunky, as I was basically coming up with the idea almost as I went along. So, what do you think, sirs?