That is up in the air. Scott had reported a 5 LNB dish is coming ... under the new legislation that D* is lobbying in the House, all sat providers will need to provide stations from a single dish. We may all need one. But for now we're all set with the Phase III dish.
Last I checked, MSGHD was a 'cable only' channel delivered only to Cablevision customers over fiber. Until it is distributed over sat, I wouldn't bet on it (something in the law about if it's delivered over fiber, the channel owner doesn't have to offer it to DBS providers).
If D* were to get it, like someone else in the thread mentioned, it would be after the Spaceway birds go active in mid-2005.
I don't think a new dish (aside from the phase 3) will be necessary, but I could be wrong.