Swamp2, nice topic.
I think we still cannot know for sure. The argument that a 3.5l I6 TT N55 will not be able to rev high is quite important. Before there were rumours of S63 with two cylinders less, so a 3.3l V6? The problem is that is would be at 90°, and that the turbos would be in the vee, what is not the best thing for a car like M3. The other solution is the 6.0l V12 of the 760i F01. So cut the engine in two to get a 3.0l V6 60° with the turbos outside, but now is the V12 basis M worthy? If the M3's engine really bases on the N55, it will be a true M engine, eventhough turbo, because it will have to undergo ALOT of modifications.
Now to the weight, the new BMW's did not get weight reduction, but just less weight growth. Only the X3 is 30 kg lighter than the previous generation. In this way we can expect the 3 Series F3X to get about 50 kg lighter. This would mean a 335i F30 would weight 1550 kg (EU) compared to todays 335i E90 that weighs 1600 kg (EU). If the M3 F32 is based on a TT I6, and not a havier NA V8, it will weigh 1550 kg (EU), what is 100 kg less than todays M3 E92, and it would be slightly less than the previous M3 E46. Yet I doubt if the weight difference of the engine it that significant:
N54: 188 kg
N55: 184 kg
S65: 204 kg
I expect S55 to be about 185-190 kg. Will this change much?
Now, there was an M5 CSL that made the N-Ring in 7:50 min. I expect to M5 F10 to make the N-Ring in less than 8:00 min, to come closer/beat the Panamera and the CTS-V, that so to say put the benchmark of the fastest sedan.The todays M5 E60 make the N-Ring in 8:12 min, and the M6 in 8:06 min. If to follow this that the M6 is about 5 sec faster, than the M6 F12 will make the Ring closer to 7:55 min. And as the M3 E92 is faster than M6 E63, so the M3 F32 will be faster and might do the Ring under 7:55 min, closer to the time of the M3 CSL E46 and Carrera S 997.
The M3 CSL/GTS (I would prefere CSL), could then lose another 50 to 75 kg and so weigh about 1500 kg (EU), that would be 1425 kg (DIN). For reference the 911 GT3 RS weighs 1380 kg (DIN). This M3 GTS/CSL might do the Ring under 7:30 min:
M3 CSL E46: 7:50 min
M3 GTS E92: 7:40 min
M3 CSL/GTS F32: 7:30 min
Now it is an impressive time, but till that day, we'll have the new McLaren MP4-12C, new 911 (998), new Gallardo, 458 Scuderia and so on, so the time will be close to 7:15 min, the new benchmark, 7:18 set by the 911 GT2 RS (997).
If M get the right engine in the M3 F32 is will be a very good car for sure. About looks, it is also very positiv, when you look at the new interiors, 5 Series F10, 6 Series F13, Z4 E89, and outside it is also so, 1 Series M is has very nice aggressive design cues.