It's not a bandwidth issue, at least not for SCRYPTmail. I believe the issue for most is prioritizing security, privacy, and the features with the most user demand.
I believe your request is represented on
SCRYPTmail as Email Export with 0.78% (5 votes) in the "what features should we develop next?" poll.
@SCRYPTmail might have more to say about it. I imagine it's possible to have an "encrypted thing" that could be generated and exported to your computer that contains all of your data. It would also need the "import" created.
Maybe that "encrypted thing" would replace your account, not add back whatever was lost since it was created to the current version of an account.
Also, for
@SCRYPTmail , I imagine this would be a premium feature. No worries, I think you're going to like their payment interface. I'm going to have blog up soon with a preview. Stay tuned!