Well, you need about $500,000 to setup a new domain extension.
And they have to be approved by ICANN and I don't think you can just create one when you want.
Plus you will need to have some department to handle it.
I don't think at the moment a .coin or .bitcoin extension would generate great revenue for the owner...
However, I'd love to have a .bitcoin or .coin extension to register some domains
owh i just know about create new domain, so i can makes my own domain if i have $500.000? like my username .kucritt or anything else? its awesome, i hope i have $500.000 to makes my own domain hahaha