I am speaking in round numbers here so please do not flame me. The M4 is supposed to have the weight of the E46 M3. Current M3 around 3700 pounds and E46 M3 around 3450. The 250 pound weight loss is supposed to come from light weight subframes for the front and rear.
I think I heard the subframes will be out of aluminum which would improve chassis stiffness, and with the usual M suspension components in aluminum and maybe a few light weight body parts.
The current N20 weighs around 150 pounds less than the N55 and is shorter improving weight distribution. The M2 is supposed to use the 1M recipe of stuffing the M3 subframes and suspension right into the M2.
With 400 pounds(250 from subframes and 150 from the engine) gone from the 1M it is very possible to see a 3000 pound or less M2 with much better weight distribution and lower polar moment, all great for responsive handling.
I love that the inline six is so smooth and well balanced that it does not require balance shafts with there added weight that effect engine responsiveness, though BMW does it with lower weight than most. So I do like the idea of an M2 with an inline 6.
But with the right 4 cylinder at around 350 hp, 3000 pounds of weight, and better weight distribution, this may be the most fun street M BMW has made.