Re: "We may see a market for paid mobile OSes start to develop."
How about we make that paying for a specific service such as email? In that case, yes. I pay for a domain and for someone to provide an email service for that domain. It gives me the freedom to choose not to use an ISP email address and hence to change ISP if I wish and also freedom from having my activity tracked by "free" email providers.
I need to have a gmail address as the system ID for my Android phone. It's actually a garbage address with no meaningful personal ID attached - and now Google seem to want me to provide its profile with a date of birth on "legal" grounds. The legality of that demand seems to be negative under GDPR.