Very true. When it comes to the resource intensive development features in 3L they can actually be disabled. But also this is partially a bet on the future, a bet that hardware resources will continue to become less constrained at all levels. Of course that is not for sure when it comes to that but it seems more likely than not that we will continue to advance in some ways. It's important though to start work now so that we are ready when the time comes.

Regarding batteries, the real issue there is how often you wake up the hardware from low power states. An OS like 3L could actually control that better than what we have today and give us better battery life.