[Dayshine]

And an interesting follow-up: Would this not continue to apply in an ongoing basis?

Just because you've lost access doesn't mean your gmail doesn't continue to receive emails, and if those emails are considered personal data, what stops you continuing to send data access requests to help yourself migrate?

[Beta-7]

How fast does Google respond with your data? I know Facebook's data export took me at least a week last time I did it (back when they first announced it). Most service's email confirmation codes/links have an expiration timer that is pretty short. If Google were really malicious they would just make you wait a week, or more, until they "gather all your data" making it not possible to migrate your accounts.

What should be possible, though, is to migrate your account without access to your email. For example make the user save a special TOTP secret that will be used only for dangerous actions and not just for logging in.