Has it been announced what alignment this will follow?
Metro Rail Tunnel/Metro One/Metro Rail Capacity Project follows the original plan of tunnelling from South Kensington to South Yarra via Arden, Parkville, CBD North, CBD South and Domain. It would link the Dandenong and Sunbury Lines together and would allow Frankston and/or Sandringham trains to utilise the Caulfield Loop.
Why call it CBD North and South Seems to overcomplicate the thing.
I agree, if it goes via Swanston St I'd just name it the same as the adjacent City Loop stations unless they build it under Russell St cause apparently closing Swanston St for 3-4 years would be like the Berlin Wall :|
EDIT: And regarding the NorthEast Link, I'd much prefer that over the EastWest Link