If you were hankering for more bent coppers and angry, tense standoffs in poorly-lit police stations, you're in luck.
BBC released a trailer for new shows in 2020 and, sure enough, 'Line of Duty' Season 6 was among the shows mentioned in the trailer. Generally speaking, 'Line of Duty' tends to go every other year with the exception of Season 3 and 4. However, given how successful Season 5 of the show was, it could well be the case that demand has moved it up a year.
The trailer released by BBC for its 2020 schedule features a blink-and-you'll-miss-it moment with DI Fleming, played by Vicky McClure, but no specific mention of a date in 2020. Only just last week, in fact, Martin Compston - who plays DS Arnott - posted a screenshot of the script from the first episode of the sixth season on Instagram.
Generally speaking, scripts don't go out to cast until they're ready to begin production, so it could well be that you might see 'Line of Duty' in late 2020, if not sooner. Here's the teaser BBC posted late last night. The 'Line of Duty' shot is around the 30 second mark.