According to latest rumors on CR, along with RF 70-400mm f/4.5-5.6L IS USM lens coming in 2020, Canon will also announce two inexpensive RF mount lenses.
The first one is an f/2.8 pancake RF mount lens, similar design to current EF 40mm f/2.8 pancake lens. This lens is rumored to be announced in early 2020. Could coming also with EOS RS high megapixel full frame mirrorless camera.
The second one is the RF 50mm f/1.8 lens, similar design as current EF 50mm f/1.8 IS STM lens. Currently no release date info about this lens. Could be in later 2020.