Here are first images of upcoming Panasonic L-mount tele converters: 1.4x and 2x. The official announcement will probably on May 31st, 2019 along with upcoming Panasonic S1S full frame mirrorless camera.
Panasonic has officially announced LUMIX S L-mount lens roadmap today. In addition to S Pro 50mm f/1.4, S 24-105mm f/4 Macro OIS, S Pro 70-200mm f/4 OIS that have already been announced today, Panasonic will launch 3 more new lenses in 2019 – a 24-70mm f/2.8, 70-200mm f/2.8 and 16-35mm f/4 – plus 1.4x and 2x teleconverters. There will be 10 lenses by the end of 2020.