To celebrate the 20th Anniversary of FL Studio, and comfort the superstitious, the next major release will be FL Studio 20, in 2018.
How will numbering work after that? Numbers will probably represent the age of the program, at the time of the last major release.
The FL Studio 20 betas is available here. Disguised as FL Studio 12.9.
FYI: Just as with FL Studio 12 (what's new), all the features we have discussed for FL Studio