Comex summarized my concerns quite well. I am almost entirely concerned about the first point in that summary, rather than the second.
I don’t buy the argument that the syntax is fine because the ?. operator is relatively unknown. If we want Rust to be a language that lasts more than the next few years, that won’t stay true. Rust’s ? operator will surely be even less well known, and by differing from the PL community norms, the language will forever have different behaviour from its peers. That adds cognitive load.