As it is javascript is the number one reason for shit battery life, I don't want to make that even worse than the days of flash which its rapidly already become today.
Faustian bargains like that aren't a great definition of progress.
Fundamentally the issue here is energy consumption while on battery. Without a way to say: a site can use N% of battery and then hard cap the usage down to a trickle and alerting the site that the user has limited energy resources available, I think this is a non starter.
Similar to when you are on LTE you don't want to use up limited bandwidth for say 4k video and want to say: you know what, I'll deal with this later and not go over my monthly allocation, the same applies here.
Is that view that unreasonable?