Maniacmechanic1 is dead on. You are asking about details that we have zero chance of knowing until on or after debut day.
However, regarding the weight - The only inherent opportunity for reducing weight versus the C7 comes from a few POSSIBILITIES (read: MAYBEES). Assume for the sake of the following that the 'basics' in the C8 are the same weight as those of the C7. Seats, dash+components, steering wheel, assortment of airbags, tires and wheels, body+glass, engine, corner suspension assemblies.
1. No driveshaft or heavy enclosed tunnel. Even if a boxed tunnel is used to add to rigidity, it would be much shorter than the C7's and could be just a tube and possibly a Carbon Fiber tube carrying wiring harness and probably cooling fluids from a front radiator (seems likely given the large openings in front fascias).
2. IF the DSG tranny is the only choice for transmission, the clutch peddle, clutch linkage, are gone and replaced by a couple of SW paddles + wires.
3. Because the C8 frame is being designed up front with consideration for MUCH higher eventual power and with variable displacement resonation consideration, there is potential for some weight savings in the StingRay and Z06. I would guess that these two will share 95%+ of the same chassis and, if possible, the extra strength for the expected 1000 HP Zora model will be added in places the GM Cray Computer told them it is needed. IMO, there should be an opportunity for 75-100 lbs of weight savings in the frames. Keep in mind that the rear sub frame now must carry the engine, transmission, axle, suspension, and more breaking torque than in the past.
4. I'll list the body and glass, but I really don't see much opportunity there other than the use of more CF and possibly use of polycarbonate (not likely as exterior replacement for glass, but possible between cockpit and engine).
5. Will the new DSG+electronic Differential be lighter or heavier than the C7 manual trans+electronic Differential? We have no way of knowing. At this point it go either way.
6. Less exhaust tubing - only a few lbs. more than off-set by the cooling tubes and fluid going from front to rear.
7. New Fed safety requirements since the C7 2014. I have no idea if there are any, but new ones must be incorporated into the C8. Obviously, NOT a weight savings, but an addition.
One of the biggest questions, IMO, is exactly how many changes (read; added weight) will be needed to support the Zora. Building the Sting Ray and Z06 with Zora-needed heft would be wasteful, costly, and unnecessarily hurt MPG and performance.
What did I miss?