Based on things I have heard very recently, I do not believe this timeframe to be true. I've heard everything on TNGA-F has been pushed back another 12 months to accommodate a new, particular powertrain. Time will well.
I'm not particularly surprised to hear that. The first TNGA Toyota (the current Prius) was delayed about 6 months from its originally-intended release date, and the postponements have just cascaded from there. Particularly hard-hit by this have been the body-on-frame TNGA-F and the Yaris' TNGA-B.
I keep a running tab of Carmaker1's predicted timetables for new-generation (or major facelifts) for Lexus and Toyota vehicles, which I update as he provides new and current information. 2019 seems to be a relatively quiet year (Mk5 Supra, 12th-gen Corolla sedan and 4th-gen Highlander are just about all the new-gen releases) followed by a 2020 which seems to have an excessive amount of new-generation releases:
4th-gen Sienna (March 2020 start of production / 2021 model year)
2nd-gen Lexus NX (July 2020 start of production / 2021 model year)
4th-gen Lexus IS (July 2020 start of production / 2021 model year)
Land Cruiser 300 / 4th-gen Lexus LX (Start of production sometime between July and September 2020 / 2021 model year)
3rd-gen Tundra (August 2020 start of production / 2021 model year. May leapfrog LC300 / 4LX as first TNGA-F product)
I fully expect some of these dates to be pushed back. Which ones is the $64,000 question, but I agree with Gecko that the BOF TNGA-F products are the likeliest to be rescheduled.