But is it possible for the users of different services to create the same domains in the Ethereum blockchain resulting in a collision? Are they offering the domains in the one namespace of the entire Ethereum or in their own namespace?
Is there Ethereum blockchain-wide coordination among them or are they just selling their own proprietary NFTs of domains that are not universally nor uniquely identifiable?
For example, could there be another ENS-similar service, e.g. DogeNS that is also able to create xxxxx.eth names? That will lead to a lot of identical names with those owned by the registrants of ENS?
This is absolutely possible because there’s no central Ethereum-wide registry. Every project deploys its own smart-contract that acts as a registry. It all then boils down to how community supports this or that registry. Currently, all libraries resolve .eth domains through the ENS registry contract and it’s unlikely that they’d change that in any time in the future because that’d cause a lot of confusion. However, there’s nothing that prohibits dapps or wallets from using a different registry for .eth domains. But it’s still a strange thing to do because they’d confuse their own users and will lose their loyalty.