It's pretty common for each generation to be one tick faster than the last, so a 1080ti will equal a 2080 and an old 1080 will be close to a 2070. It can be a bit more or less, but that is the general rule.
"But they don't have ray tracing."
It will be a while before you "need" it, and while Nvidia has made it easy to implement, as a software developer you can't expect people to buy a $1000 card just to play your game if you want to be successful, but more importantly, you can't do full screen raytracing with a 2080ti, they don't have anywhere near the power to do everything on the screen. Which means it's only going to be bits and pieces. Also, Nvidia has rarely rolled out a major new feature like this and had it work smoothly right out the gate, it will need a revision or two before it really becomes usable for the masses.
Remember, other than refresh rate, video cards do not make the game faster or look better, they can only bottleneck what is there. If you are already on max settings and getting good frame rates, a newer, better card is going to be the most expensive, most boring upgrade you have ever made. You can say you are future proofing, but if you're not bottlenecked, why pay the tax for such a bleeding edge part when you could wait for the bugs to be worked out, games to support it and prices to settle.
If you can get a 10xx series card cheap, new or used, buy it.
If you want new, you may want to wait for Black Friday deals. If buying used, try and get cards that were not used for mining, and beware the cheap Chinese clones. Some work, but for how long, while others are disasters, with the wrong firmware being loaded, fake device ids and more. Also, try not to dismiss the used Radeons right out the gate if you're not using 4k, while not a GTX1080, you can get some killer deals on an RX580, which will run most anything (they sit between 1060 and 1070) and that could buy you some time waiting on an RTX card you can afford. I recently got a lightly used 580 for a less than I could get a 1060 that was used for mining, just watch out because the 580 was one of the preferred cards for mining.