You seem to be totally unaware of all the problems with LVM (search the forum).
You seem to be unwilling to admit that your invention is not perfect. Your cure to the LVM problem creates a new set of problems.
One user reported how the new method corrupted his guest filesystem, LVM snapshot never did this as far as I am aware.
Never had a LVM snapshot method cause the guest to stall when backups had issues, new method does this.
Numerous people have observed increased load with new method, this I predict will not be resolved with patches to KVM live backup.
I think you should use a fast local disk for such backups, and use hook script to transfer result to slow storage.
This was not necessary with LVM snapshot backup. Yet somehow you expect me to believe that this new method is vastly superior.
Both methods are flawed and have their issues, neither is a perfect solution in all situations. One can stall the VM when things go wrong where the other does not, one uses more disk IO than the other, one requires writing external scripts to avoid decreased IO performance the other does not.
This is why I advocate allowing users to pick the method that fits their needs the best.
Maybe at some point in the future the new method will be much better and LVM snapshot will not be needed. In the meantime people need to be able to reliably make backups without risking a stalled VM or causing the VM to run slow.