The last thing you want to be doing is saying, no no, not .com .io. People will just get confused. Also, because of how most of the search engines work, you may wind up pushed down the results unless someone adds 2-3 extra terms to find your specific brand. For example, an overly dramatic example, but pick Microsoft, with all their history and branding out there regardless of if you could use their name in a brand, would you really want to compete against it?

So even though you might be able to trademark it and get a domain, it doesn't make it worth it. Pick something totally unique that you can stand alone as a brand on. Otherwise you will spend a lot of money setting up marketing differentiators.