> If I need some namespace for my open source project, I can go and register a top level domain
One common question here is: if you have an open source project, why do you need a TLD? Why is that special? the TLDs are designed into the DNS space and exceptions aren't cheap. Registering a domain under .org, or .horses is cheap compared to the $185k. And using something under .alt is free. Justifying the need for a TLD is difficult when there are other options.
>> The real thing is: why are alternate spaces even caring whether or not they look like the DNS and have a TLD? > Because they want to be supported by existing software.
That's exactly the point I was making: the goal is to get the cheap way out trying to register part of an existing landscape rather than inventing a new universe. If the new universe is that much better, then everyone will want to deploy it anyway. As the web browser market will tell you, their applications (the only ones that most people care about these days [not me, mind you]) update ever 3 months. Getting them on board with a new universe should be trivial! In fact some browsers already support alternate spaces. Green-slate designs are often much cleaner and better when people aren't trying to do a mix of revolutionary and evolutionary approaches.