Tsui Hark (The Raid) will once again direct. There’s currently no information on whether Detective Dee and the Four Kings will be a sequel to the 2010 Andy Lau film (Detective Dee & the Mystery of the Phantom Flame); or if it will be a follow up to 2013’s Young Detective Dee: Rise of the Sea Dragon, which starred Mark Chao.
Since Kenny Lin (Rise of the Sea Dragon) is the only confirmed returning actor so far, a “sequel” to the latter is our best bet. Of course, there is still the possibility of a time paradox-infused script, featuring both incarnations, according to a 2014 interview with Hark.
Detective Dee and the Four Kings shoots in 2017/releases in 2018.
Updates: In addition to Lin, AFS reports that Mark Chao, William Feng and Carina Lau will return for Detective Dee and the Four Kings.