AMD's AM4 should be compatible with Zen2 but Intel's current 1151 socket boards will not support CoffeeLake.
Don't buy Ryzen and an AM4 motherboard just because of that though.
- Zen 2 might require AM4+
- If AM4 ends up being compatible an old AM4 board might or might not get the BIOS update it needs
- Zen 2 might or might not be a better CPU than whatever intel is offering at that time.
If Ryzen and Coffee Lake are roughly equal for your needs, then using AM4 possible future proofing makes sense as a tie-breaker.
My philosophy: Decide which CPU meets your needs now and for the next few years. Pick a decent motherboard for it. Use it for years. By the time I've upgraded in the past I've wanted a new motherboard for newer USB, SATA, faster DRAM etc. anyway.
If you ask me you can't really go wrong with Ryzen right now... plus Intel keeps shooting themselves in the foot by constantly requiring new chipsets to be adopted by those looking to update.
well it's a hard pick but since intel is off the board for upgradability then ryzen looks like the better choice. My only concern is that performance is not as fast as a 7700k gaming wise and if ryzen 2 can close that gap a few percentage points I can always upgrade to that with out much out of pocket expenses. Yes coffee lake is supposed to be a much bigger leap in performance but I do not think I can wait that long for it to drop. So this small upgrade path is swaying my decision.