It's interesting examining the problem of supporting stability for BPF, the docs technically do make some ABI claims about for instance about kfuncs being potentially subject to change while BPF helpers are not and are considered stable.

It's difficult to reason about verifying a program for memory management in BPF. It seems unlikely that on the first try we'd get something flexible enough for all use cases, yet that doesn't fundamentally break the "safety" provided by the verifier. So I see why this has been a thorny topic.