Either Gatiss or Moffat said that the reason they chose Rupert Graves for Lestrade was because you could imagine his Lestrade starring in his own television series if Sherlock weren’t in the picture.
I kind of want to see that show. It’d be Scotland Yard CID from Lestrade’s perspective, where he and his team BAMF it up around London and solve cases on their very own. Sally Donovan is the badass second-in-command, Anderson’s the guy who works miracles in the lab, and Dimmock and his guys come in whenever they need additional police support. Gregson is the jackass rival in the department who keeps trying to undercut Lestrade and make him look bad to their superiors, but when push comes to shove, he’s a damn good cop.
Every so many episodes, Sherlock wanders through on a guest appearance where he’s That Guy who periodically turns up on the crime show as a character foil to make everybody’s lives a living hell while they try to get their jobs done despite him. John could turn up in the second season to shunt him from quasi-villain/complication to more of a recurring supporting cast role.
And then the third season ends with the blockbuster two-parter where they’re all in over their heads on the Moriarty case. Sherlock guest stars, regressing to his previous quasi-villain status (AND PERHAPS BEYOND, omg was he the bad guy the whole time?!), but at the denouement he has his moment of ultimate redemption and jumps off a building to save Lestrade’s life. They’re all very sad but it’s also touching because he turned out to be one of the Good Guys in the end. And the producers can save money from writing that guy off the show, because he was starting to star in everything and they really couldn’t afford to keep him on the budget constantly.
It’s like it’s straight out of NCIS.