I think it's got to be very useful for protection from extortion too if it can be designed so even us ourselves don't have access. For example putting half of the key out of reach to us somehow?
Yes, you can always reschedule an encrypted email for yourself with the private keys, saving and protecting a part of your Bitcoins for the future. It's like a true savings account. Great outcome!
But this only works if you, after send the future message, can't access the contents anymore. (Perhaps only change the date of arrival, just for later, not earlier.) And you can set each date change a limit, like 5-10 years later max. So nobody (attacker) can force you to set the date for, like, 100 years and make you lose your coins.
You can set more than one future email provider, just in case. And set the time you want to be protected (even from you).
If you change your mind, you'll have to turn off the automatic rescheduler and wait for the message at the last chosen date.