On the lethal vs nonlethal front...
Making the whole game that way? Probably unfeasible, also unprecedented in the series for the whole game to behave in that manner. Also generally unwanted for my part.
Making a mission or few? As someone mentioned earlier, the gas bombs was a nice touch to give paragon/renegade a bit more flavour.
In that context, of giving you the option here and there? Hells yes. Playing my renegade Infiltrator of course he just put a bullet in everyone infected. He didn't have time to deal with some silly grenades nor sort out what to do after the fact. They were infected, they needed to die. There was more at stake than a handful of colonists even that early on, and he knew it.
My Paragon Adept though? She weighed her conscience. My infiltrator felt that time was against him (it was) and made the hard calls under that premise. She felt that numbers were against her, and every body saved was a body she could stand against the reapers; even at the expense of time.
Neither were entirely right, and neither were entirely wrong. Both saved the galaxy so /shrug. But the point being, I appreciated the choice.
I don't really want "Deus Mass Stealth Effect: The EnReapening". But a mission or two, or few, could be made to help give meaning and impact to your choices, be they blue or red.