This is a really cool idea, but an email account? That seems pretty unsafe to me. Accounts can be closed at random, the email provider can go under.
I don't know, maybe it's not better but I think I would feel better with a flash drive or something physical (which I would backup and replace every so often).
Email is the lowest friction for me, I can send something from pretty much any device and it is easy to access for them in future.
There have been a few comments on the long term accessibility of the account, like you mention. So I think it could be a good idea for me to look into doing a scheduled backup from gmail to a drive or other data storage option.
I don't know, maybe it's not better but I think I would feel better with a flash drive or something physical (which I would backup and replace every so often).