Although this is an appealing idea, I don't think it is realistic. Lobbying would destroy any legislation almost immediately, and there would still be the issue of competing standards.

I think a more achievable version would be that any online service which maintains user data must provide a method for a user to retrieve that data in an open-source format. Some companies would deliberately obfuscate formats, such as calendar appointments as JSON rather than iCAL or another existing standard, but I think it would give users more control than they currently have.