Imagine you bought rtx 3090 today, then after a couple of months later its Super version is released with 20% of more performance? it would be a slap on your face. so don't buy any Nvidia card until its super version is out.
That's extremely unlikely. Because even if you take the 2080/2070/2060 Super launch, those cards came out at least six months after the initial non-Super GPU. To be specific:
2060 Super came out six months after the RTX 2060. This was purely to counter AMD's RX 5700/5700 XT launch. (Also, price was $50 higher.)
2070 Super release was nine months after the RTX 2070.
2080 Super release was ten months after the RTX 2080.
Your 20% more performance claim is way off as well. The 2060 Super is 13% faster than the RTX 2060. The 2070 Super is 12% faster than the 2070. The 2080 Super is only 7% faster than the 2080. I suppose you could be referring to the 1660 Super, which launched seven months after the 1660. Or the 1650 Super, which came out five months after the 1650, but those are in a very different category from the RTX 3000 launch -- budget to midrange, not high-end and extreme.
Plus, the RTX 2080 Ti never got an updated 'super' version, and the 3090 is clearly going after that top-of-the-line classification. I don't think you'll see any 3000 series 'super' cards until at least 2021, if ever -- that or the Super branding will be present at launch. I'm still anticipating one of the cards being called "Ultimate" or similar, though -- RTX 3090 Ultimate would certainly make the "Ultimate Countdown" accurate.
If you think you'll buy an RTX 3090 GPU, the best advice I can give is to buy as soon as the price reaches a level you're comfortable paying -- or just don't buy it at all, because it's too expensive for your budget. For those that have the money, the RTX 2080 Ti cost $1200 at launch, and for nearly two years the only faster GPU available was the $2500 Titan RTX. I strongly suspect RTX 3090 will be the top Nvidia consumer GPU for at least a year, if not two.
Still not worth $1500-$2000, but if you must have the 'best,' that's where it's likely to hit your wallet.