Right now there is no tank water heater ( gas ) which comes close to the 0.82 energy factor needed for rebates. Things like the standing pilot and convection losses up the flue prevent that. Kind of like there will be no energy star stoves or clothes dryers. They are designed to do one thing...make things get hot, and you can't cut back much on that, unless you want raw chicken and wet clothes!
At some point, someone will offer a residential heater with fancier heat exchangers, flue dampers, and whatever else it takes to get the numbers up. But they will cost a lot!
Even a power vent today does not come close.
I am not a fan of tankless. Some love it. In my experience overseas, tankless were located right at the scene of the crime so to speak....a small unit literally IN the bathtub, right next to the washing machine , etc. This works well. We will probably see more of that in new construction going forward. As a retrofit, I see Clint Eastwood syndrome..." you gots to know the limitations!"