The murder of SLI made me so angry. It was so wonderful to be able to buy a card, then a few years later buy another of the same card for a bargain price and boost your performance by ~60%.
Usually by the time you could buy a high-end CPU replacement, it was a "better deal" to just replace the entire motherboard/CPU combo and get a whole new computer. But a second video card, some more RAM, additional SSDs, those made sense.
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".