There are no automatic upgrade in DX12, mainly because DX11 is already very capable (also, current rendering is already multi-thread). DX12 provides a lot more APIs that allows changes on architectural level, but that would require Asobo to do major rewrite to take advantages of those.
As Asobo already stated directly, current DX12 work is more like a port: making sure everything is running as in DX11. They have also stated that the performance gain won’t be from DX upgrade but from parallel optimization work that will be released at the same time.