X79 and X99 are only obsolete if they don't do what you need them to. Don't let Intel or AMD tell you your shit is obsolete. Don't fall for marketing.
It's why I got X99 despite being basically at the end of its life. Same for 5820k. And I even got a golden egg with decent overclock at stupendously low voltage. If Intel will go price crazy with X299, I'll go with AMD for sure. In fact I'm almost certain my next CPU will be AMD. Even if they are slightly worse, they are a viable option now. With Bulldozer, even though I wanted AMD, I just couldn't bring myself buying a sub par CPU. But Ryzen is none of that and if they continue optimizing it well in the future, they'll be doing just fine. I also hope AM4 will live as long as AM3+ has.