Wait for the new gpu, but get ready for it's high price.
The new GPU will have to mine proportionately better than the 1080TI in relation to its price in order for the wait to be worth it. Otherwise you are paying a crazy premium for a card that is only giving a 20%-30% boost. The new architecture would have to pull a rabbit out of the hat in order for that price to be viable.
Even an used 1080ti card price is still high.
philipma1957 mentioned they have good prices on used 1080TI. You can get them for very good prices right now, because people are getting ready to upgrade their gear, worried about ASICs ruining big altcoin mining, dips in prices/profitability, etc. The list goes on and on, but you can get high-quality, gently-used cards for great prices right now and get going. You'll only make a few dollars a day per card, but even at that rate you'll ROI in a few months; if the price goes back up to $20,000 or any of your altcoins have a spike then you will be in good shape. Even if it doesn't, you'll be able to sell your cards off for maybe even a profit.