With technology the way it is, there's always something better soon after. Which means the decision can be delayed indefinitely until it's decided enough's enough and you end up getting what you can afford at the time.
That said, the 8th gen Intels do look really good. But stock shortages don't help and it seems to be early 2018 before that situation is rectified. How soon after will the 9th gen be released? No idea (rumours suggest late 2018), but it does make the 8th gen feel shortsighted and limited in a sense.
Generally, I would consider how dissatisfied you are with your current PC and whether it's enough to make you think you can't tolerate the performance anymore and need an upgrade. (I built my new one a week before the 8th gen reviews were out.)