As time goes on with eMTB's things will become more clear in regards to their power to weight to amount of range ratio. Handling issues for both up and down needs will balance out also. As in is it important for overall handling to have the shortest chain stays or the lightest weight? Personally after many miles of riding my POS kit bike on varied terrain my observation is that it is still not the bike, but the rider who will ultimately make the difference.
Energy use while riding as noted is dependent on the overall weight of the bike/rider and their demands on the system. Ride in turbo all the time and you'll use more wh/mi, ride in eco all the time and you'll use less. The balance is to use the energy to accomplish what your personal goals for any given ride are and that only comes with experience based on what you are riding and where you are riding it.
Wh/mi is the equivalent of mpg in the world of e. If you have a 500wh battery and use 10wh/mi you could figure that you will get 50 miles of range and that seems to be the calculation that many manufacturers base off of. But as BCS noted voltage sag reduces the available energy as it is depleted and that has a huge effect on overall range as the ride goes on.
In the real world 15+wh/mi is more the norm dependent on the factors mentioned so right away you are down to 33 miles of range and accounting for voltage sag probably more like 30. There is really no way to fudge the numbers here as all the current mid drive systems run at about the same amount of efficiency but are also dependent on the amount of energy/watts the rider applies while under way.
As far as the upcoming switch from 18650 cells to 2170 cells it will be the most significant change in the foreseeable future for eBikes. Here is a comparison I made up last June when I started to look into this based on a 48v/15ah/720wh battery:
Performance numbers aside, which the 2170 cells obviously outperform the 18650 ones, the amount of cells it takes, 91/39, is the reason for the 21700 battery to weigh less yet perform as well or better.
The 18650 cell weighs 48g and the 2170 weighs 68.7. So the 18650 battery will weigh 9.6lbs and the 2170 5.9lbs.. This is a major weight reduction as noted by BCS while at the same time providing a better overall battery.
Unfortunately going forward because of the cell size difference it will be a hard fix to adapt 2170 cells to existing enclosed 18650 cell systems. I don't think the manufacturers are losing any sleep over this because it means that folks will be back to buy whole new bikes that want the upgrade and that is how the bicycle industrial complex rolls.
That Trek looks like a fine bike though, very sleek and sexy and I'm sure will provide many miles of smiles, long chain stays and all.