Sell the Ryzen and use the funds towards the 8700k before the ryzen has absolutely no resale value at all.
Errr... what? I think you got tad ahead of reality there. Now, I would also love 1700s being sold for $50/piece everywhere, that would be lovely. So I kind of understand your youthful enthusiasm, but sadly wishful thinking never made the wishes happen, alas.
It's more likely that these won't drop to very low prices for years. While they don't provide high absolute (single-core) clock OC like i7-2600K, with the eight cores, they will probably represent something between a Core 2 Quad 6600 and i7-2600K in moral longevity. And prices of 2600Ks weven't funny as far as this spring at least, considering we're talking 6 years old chips with serious chance of high-vcore degradation from long-term OC.
Anyway I would probably not do this, it's too soon for upgrade and the difference is too small. I think putting money in something else would be more fun. VR headset, huge 4K screen, some silly-fast SSDs if it is for bragging rights (seriously speaking those probably only matter for benchmarks), or some non-PC/HW items actually. I would probably be interested in the VR helmets, I'd like to try the Everest simulation some day, the 8000s are fascianting but one doesn't really get the feel of what it is like being on it, from TV.