Interesting thread. I don't think the next gen will be lighter than the current, and the following gen won't be lighter than the E46, but you are right, the future will be about shedding pounds, and not about adding more power.
And yes, I would take a 414 HP M3 with less weight over the alternative you mentioned.
2008 E92 M3 6MT, AW/Blk Ext., brushed aluminum
2006 E46 M3 ZCP 6MT Carbon blk/blk(sold)
2001 E46 325Xi 5MT Jet Blk/Blk (sold)