You'll then also have the usual limited availability of the high-end models for the first few months. It could be the better part of a year before you can get your hands on a 10700/10900, so you should consider whether you'd rather upgrade now to a 9700/9900 and enjoy the games that you're currently playing more.
The next generation won't offer anything significant other than two extra cores on the top-end model. By the time that actually makes a difference in gaming, I'd say it's a fair bet that you'll want to upgrade to a platform with DDR5, PCIe 4, etc., and a much more efficient 10+ core CPU.
Do you really think it'd be that long?
If I waited I'd be looking at the 10700K which is going to be pretty much the same as the 9900K, maybe with slightly higher clocks but nothing major. Whilst the CPU may end up being cheaper in the long run as it's repositioned as an i7 rather than i9, that's only going to be after prices have stabilised and availability is good. Same goes for the Z490 mobos.
Maybe I should just jump to 9900K/Z390 now? :/