Whilst that's true, when someone decides to purchase a domain, why would they buy a .tel when there's other namespaces with more freedoms? I'd be surprised if .tel takes off in preference to .id.au in Australia for instance; — I know which domain I prefer and pay for.
* The suffix indicates the capability. It wouldn't be obvious that andrewtj.com contained your contact records. I'm not sure how you could change public perception of .com/etc, but you at least have a shot at it with a TLD exclusively for this purpose.
I'm not sure that this is as practical a benefit as it sounds. If you were to ask me what my ".tel" is and I responded, just use "andrew.tj.id.au" you'd plug it in and use it. If you were to use andrew.tj.id.au on a computer, you'd likely consume it without even thinking about it.
* TelHosting providers are obligated to provide standard public APIs, and there are also specs for consuming structured data from DNS. Would you use these, or create your own?
* For people who do own a .com they most likely won't be running their own nameservers, so you'd have to persuade nameserver operators to agree on API specs and run your management software.
* .tel has a system for brokering encryption keys used to encrypt/decrypt records - if you want privacy you'd need a system like this.
I've written a DNS server and run a DNS service so it's a bit disingenuous for me to answer these questions. That said, I would and am considering providing the infrastructure for myself and others.
* Using a common namespace offers us a publicly accessible zone - convenient!
I'm not clear on what benefit this outlines?
* Marketing. Hundreds of registrars selling a common branded product gives it the best chance of adoption.
* It's actually pretty hard to do by all accounts.
Agreed on both accounts. The later is part of the reason for my lack of enthusiasm for it.