I was on a team that handled a lot of things that way, and we made a deliberate, conscious shift to pull them into oncall rotations. We found that it was severely compromising work-life balance; engineers outside of the old guard thought they were expected to work most nights and most weekends, because they'd constantly see people get bonuses and accolades for some stuff they did at 6PM Saturday. I personally enjoy the "work whenever you want, play whenever you want" model, but I really don't think it works as an oncall policy.