Email is an incredibly vulnerable single point of failure. Plus the existing password infrastructure of the web isn't going away. Password managers are the best and most realistic option for most people.
I found out that when I added a backup email to my gmail that it had the opposite effect that was desired - losing access to the backup email meant I couldn't recover the account even though I still had access to the primary. I still can't get over the perverse, Kafka-esque feeling, years later. Partly because I am still logged in, yet I have no way of restoring my "ownership" and using it again.