I think this is an easy one to answer too, because I've had an idea knocking about in my head for a year or two, and if someone doesn't do it soon, I might have to. It's not a new idea idea at all. It's a licence I have in mind, and as a game it would join the plethora of "urban fantasy" games that already exist. But I think the books it is based on bring something fresh and to the genre, even if that novelty is only the idea of genius loci. I want to call that series, the PC Peter Grant books, but it seems fated to be known popularly as the Rivers of London. Its a magical fantasy, following the adventures of the Metropolitan Police unit known as "The Folly", which deals with supernatural crime. But its rooted in a very real London, which such a perfect understanding of genius loci or "spirit of place" that I knew as our protagonists drove towards a particular tree, before the even got there, where they were going. (It's the tree in the picture above by the way.)
So I see a game that's a police procedural, with magic. It'd be called Callsign: Falcon, which the the term which (in the fiction) the police use to tell each other that "weird shit" is going on. In my head the mechanics are very influenced by GUMSHOE (particularly Mutant City Blues) but a straight steal of that system wouldn't be enough – otherwise I'd have done it already.
No, it needs a fabulous magic system, that allows players to build spells out of basic based, in the books, on Newton's lesser known opus Principia Magicka. Given that its Newtonian Magick, I feel it needs to be based on some mathematical solids other than a mere cube. As GUMSHOE uses a d6, it simply doesn't have enough sides for this game. I'm attracted to the dice-pool building mechanics of Cortex Plus, but I'd want this system to be player facing, with the GM rolling few, if any, dice.
Go on, somebody write it an publish it, please!