I would guess atleast another 20 RSN's ,Also let me add that it has also been stated that there will be more channels launched at some point besides these. After the initial batch of 30 channels are launched, there is capacity for 50 more. What D* will do with them, who the heck knows.
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10 3D, and 20 PPV. Thats my Guess of what D* will do with 50 HD channel slots.