I'd think its close - they've got screenshots for SX4 and such out.
I read somewhere on cubase.net that the SX4 beta they've got runs on an intel-mac just about like SX3 (or maybe SX4 beta) does on a similar windows machine - something like that. That came from a Steinberg rep.
I'm going to be getting a MacBook Pro here in a few weeks, and I run Cubase SX3. I'm just going to run it in Windows XP Pro via bootcamp - I'm not even going to intall under Mac OSX - I've read horror stories about running it on OSX via Rosetta.
Oh well - I've got some Window's-only plugs that I use, too, so I'm not ready to fully make the switch to mac yet.
I'm pretty excited at the prospect of a nice mobile recording rig, though!