As Brant wrote....no need to ditch EF lenses as they work great with the adapter. In the shorter focal lengths there are already some great RF choices.
For birders, in the future there may be great RF lenses to be had but right now in the super telephoto world EF rules.
There is a rumored 500mm f/2.8 in the works!
Hey Canon: I would love to see an RF 600mm f/4 DO lens!