There will be few mods you can do for the new S65 and the biggest limitor is the 12:1 compression ratio.
At 12:1 compression ratio, forced induction is not going to happen for the new M3 no more than the current M5 / M6 (which has the same compression ratio). There is the Osh "800hp" twin turbo M5 for $350,000 but this is just someone with pipe dreams.
M cars come tuned aggressively from the factory so the only areas for focus for tuning is where BMW had to make compromises for the street....
- Camshafts (but you will lose that sweet flat torque curve for high end power)
- Shorter Rearend (like the Dinan 3.91)
Even ECU tunes for the M5 / M6 have yielded limited benefit. A guy on the M6 board had headers, exhaust, Dinan 3.91, ECU tune and Kelleners cams only got another 5 mph trapspeed over 1/4 mile over a stock M6.