I'm hoping Bitcoin Cash overtakes BTC in price, becomes the bitcoin and then if it does I would not be at all surprised if it reaches 40k or more in 2018. Once enough people realize that Bitcoin Cash is the upgraded version of Bitcoin adoption and investment should go through the roof.
How long it takes to flip is anyone's guess. Bitcoin Cash is way higher than BTC was last year. . . but it isn't going up as fast in BTC price as I had anticipated, I think it will reach something like 18-20k no 2018 should bring BTC prices of anywhere from $25,000. - $50,000 cos we already saw $18 - $20K, this year!
Whether it's BCH or BTC, I think whichever version of Bitcoin is leading by the end of 2018 has a high chance of reaching 40k at some stage in the year. It's only double the highest price for BTC in 2017 (so far), and at the current rates of growth we could even reach that price within a couple of weeks.
The only thing I'm unsure of is how long it'll stay high. At the moment I think the price is driven largely by speculation. We're well overdue for a "crash" to restore some sanity before it starts rising again. But who knows how long until that crash actually comes.