Unsolvable would mean that no proof exists, and no disproof exists, in whatever axiom system (eg ZF). While in some cases you can hack around this by proving eg "no proof and no disproof exist in ZF, if ZF is consistent", IIUC that's not always possible. It's like asking "when will AI be strong enough that it can always decide correctly whether a given computer program halts?"
Then again, it's fairly likely that P=?NP is decidable but we just don't have any idea how to prove it. In that case the question is more or less "what's the time horizon until AI is vastly better than humans at formal math?", to which the answer is certainly "we don't know, there may be obstacles, just wait and see".