Am not a comparative linguist by trade but thought the Dene-Yenesian hypothesis was pretty well established at this point?
Edit: wiki link https://en.wikipedia.org/wiki/Den%C3%A9%E2%80%93Yeniseian_la...
First link was proposed by Merrit Ruhlen in 98. People have opinions about him but he and his mentor Greenberg did very well received work on African comparative ling