I think it’s fine as long as the user can opt-out and have the opt-out stick[0]. My problem with YouTube is that I can’t tell them “when I’m not on a metered connection, blast my face with as many pixels, frames and bits of color as possible” and actually have that happen.

[0] I say opt-out not opt-in because the audience for ABR is people who wouldn’t know where to find an opt-in button or wouldn’t know that it exists.