SLI was ultimately killed by the rise of TAA. Interleaving frames breaks the assumptions of TAA models about the presence of temporal history. That's why NVIDIA went down the path of building a better TAA model/upscaler instead.
Games are just going to use temporal accumulation now. There is too much signal to be gained from re-using past samples. It makes things way cheaper and opens the door to extrapolation and non-uniform sampling etc. It's the least bad of all the options, and DLSS actually is quite good at weighting samples pretty reasonably. DLSS 2.5, 3.0, 3.5 and upwards are actually significantly better and that can be injected back into (non-anticheat) games and the bar will likely continue to be raised. It is a signal processing technique that recovers a lot of signal with very low "noise factor".