(Sorry for extra post, I'm using an old computer and can't write to much on the same)
If M5 gained 300 lbs and so did the M6 over the E63 M6, what makes you think magically the new M4 will be lighter??.
Now, the increase in weights you talk about are understandable and I agree with you. Bigger body, more powerful engines and added security mean a heavier car. But as someone told to me, the S65 engine was lighter, so even though the E92s overall weight was increased (I guess mainly due to security reasons, again) in comparison to E46 M3, the heaviest part of the car was lighter.
BTW, I don't believe in magic. It's all about engineering. Besides, M4 may be bigger than E92, but it wont be as luxurious as the M5 or M6... (So extra weight is not justified, this time not even by security as it was justified on its previous generations) Besides, you are not saying that those cars are way more efficient than the ones they replaced. But 90 Kg are not "such an issue" in F10, because as I said, its intended to be luxurious. But the M3 (or M4, for that matter) should start losing, weight.
If this does not happen, maybe I'll forget about getting an E46 and start saving for a used E82 while they are still around in good shape... And I'll say all this time you all were right about the new, heavy M4. BUT, if I'm right, we may have a better car than the E92 to admire =) and I'll get the E46 so I can save for a M4 or at least a 435i =)
P.S.
If it wont by any means be lighter, I bet it will at least be more efficient and aerodynamic. And before anybody says "who cares about efficiency in an M, well, we all do. Less fuel, more power. Smaller engines, lighter cars.