There had been plans drafted to finish dropping Yum 3 in Fedora now that DNF is quite mature as the next-generation package manager, but that isn't happening now until at least Fedora 30.
Fedora 29 isn't eliminating Yum since it's a fairly disruptive change at this point in the cycle, there still are some important infrastructure components depending upon Yum like Koji, Pungi, and others, among other logistics to work through.
As a result, at today's Fedora Engineering and Steering Committee (FESCo) meeting, the plan to drop Yum for Fedora 29 has been rejected. The work will likely be re-attempted and cleared for the Fedora 30 release next year.
At today's FESCo meeting they did approve the Zchunk feature plan for Fedora 29.
Today's FESCo meeting minutes can be found here.