Persistent app-accessible root greatly regresses OS security and breaks the verified boot security model. We're definitely not going to increase the number of build variants from 40 to 80 in order to provide an insecure option which would take away from efforts to properly implement features instead of doing it via hacks using apps running commands as root. If you want it you can make your own builds with it instead of us doubling the number of builds and deltas we need to make. Most of the people doing it are modifying the official builds and resigning them. Anyone who can understand the consequences of app-accessible root is capable of doing that.