Seriously, the domain fees shouldn’t be an issue. And while registering a domain and connecting it to a suitable email provider is a bit more involved than setting up a new phone number, it’s not that complicated either. People without any technical affinity will need help with both.

I agree though that there should be legal resort to not losing your email address.

Are you suggesting that everyone has a legal right to a free email address? Phone numbers aren't free either, a phone line is way more expensive than a domain.

If you think there's real demand for email portability, go into business! A service that lets you buy a domain and route to different email providers is well within the abilities of a single programmer. Make the UI idiot proof and charge a few bucks more than the registration fee.