An nvidia dev explained it in another thread, but the gist of it is:
- DLSS 3 is a superset of DLSS 2.
- DLSS 3 has three parts of this superset (Frame Generation, Super Resolution and Reflex), the only part that is exclusive to RTX 40XX is Frame Generation which predicts and draws the frames ahead of use, (this is what NV said is drawn at 120fps?). frame Gen is possible on RTX 30XX but the Optical Flow Accelerators needed for it on 30XX are slower/lower quality from what the dev has stated.
- As DLSS 3 is a superset of DLSS 2, DLSS 3 upgrades over time will continue to benefit older cards only capable of DLSS 2 as these will still gain improvements. So 30XX isn't dead in the water with "only" DLSS 2 like many are thinking.
So in short, yes DLSS 3 can still be used on 30xx, just we won't get the full benefit as we won't have Frame Generation being utilised as the OFA isn't as efficient on 30xx.
How much performance we miss out on will be shown in independent reviews. It might turn out to be only a small bump in frames in actual production titles for the 4080 cards, whereas the 4090 sees the biggest jump.
Let's see some reviews.