Nothing 100% sure about BG3, though rumors as always tend to fly around. If there will be BG3 - what I would really love also - then it wont be about the Bhaalspawn of course. Which is OK with me too, as long as the new story would be good and all that
From engine, then something new wouldn't hurt indeed. Something better and improved, with much better 3d support. As it is now, having the 3d acceleration turned on actually slows the game down, rather then speeds it up. There are also few restrictions in BG games, which come from the engine itself, rather then the rules. For example the Ioun Stones were supposed to be wearable by mages, as they were invented by a mage for the mages (free tip: King Storhm's Mask is wearable by all btw, and acts like a helmet - protects from critical hits - protect your thief, or your mage, today!).
Guess we will see. I personally WANT Fallout 3 badly as well, and as Bioware president said, it's a game they want to make as well and in new year (soon), they will tell about it even more. Cool, I just hope that it will be as good - and better if possible (which would be hard heh) - as the previous 2. We'll see what the time brings. It would be really sad if the BG as such would be "over", I don't get even half such feeling in IWD as in BG

And NWN, well, can be zoomy but it still isn't BG..