Aldous's conjecture on instability of queue-free backoff protocols

Let a queue-free multiple-access protocol have message arrival rate $\lambda>0$, and let a backoff protocol be a protocol in which processors back off after transmission attempts. The protocol is stable if its queue-free system remains stable under the given arrival process.

Aldous's conjecture. In the queue-free setting, no backoff protocol is stable for any positive value of $\lambda$.

This is the foundational open question for acknowledgement-based backoff protocols: whether any such protocol can be stable at all. Aldous stated it for binary exponential backoff, while the conjecture here asserts the same instability for all backoff protocols.