CameraJabber posted these images of the new lens and converter prototype.
And Dpreview has those images:
Here is some info about the new gear:
M.ZUIKO DIGITAL 2X TELECONVERTER MC-20
The M.Zuiko Digital 2x Teleconverter, MC-20 doubles the focal length of the master lens while offering outstanding portability as well as dustproof, splashproof, and freezeproof (-10°C) performance. The teleconverter is compatible with the M.Zuiko Digital ED 150-400mm F4.5 TC1.25x IS PRO lens, currently in development, as well as the M.Zuiko Digital ED 300mm F4.0 IS PRO and M.Zuiko Digital ED 40-150mm F2.8 PRO lenses. Not only does this teleconverter extend the telephoto range, but it also doubles the maximum shooting magnification of the master lens for unprecedented super telephoto macro shooting. This item has an expected availability of summer 2019.
M.ZUIKO DIGITAL ED 150-400MM F4.5 TC1.25X IS PRO
Development is under way for the M.Zuiko Digital ED 150-400mm F4.5 TC1.25x IS PRO, a super telephoto zoom lens in the M.Zuiko PRO series, designed for exceptional optical performance in a compact, lightweight form, along with dustproof, splashproof, and freezeproof (-10°C) performance and superb mobility. This is the first Olympus interchangeable lens with a built-in 1.25x teleconverter, which easily extends the lens to the maximum focal length of 1000mm1 (35mm equivalent). It also offers in-lens image stabilization (IS), supporting 5-axis Sync IS when operating in concert with the image stabilization of Olympus OM-D cameras. The compact system delivers remarkable portability, and the built-in teleconverter provides convenience, making it the optimal super telephoto zoom lens for sports and bird photography. This lens has an expected availability of 2020.