Thank you for the response. One correction though: unauthorized access to a 2-of-2 wallet would require exposing BOTH keys; not just one.
The point of my proposed setup is the user would really still only have to keep secure a single private key. As for the 2nd key, just assume it's exposed. You just have to make sure not to lose it (so put multiple copies in multiple wallets, in multiple cloud storages, in the blockchain, etc - pretty much anywhere except for right next to a backup of the 1st key)