If you already had a steam account then yes, sure it would just take form of your current steam account ( we would assume ). Although for those who do not have a Steam account & now have to make one that has a completely new unique name ( most likely not resembling the one they used on blizzard ). In my case I have a very old Steam account, that I barely use in which the account ID, community ID and game ID are all 3 different names ( since you can only set your game ID once, per Steam support ). The community ID can be changed at any time on steam but that is only useful for a friend to even find your account.

I'm not sure if it works like you think it works anymore, it might do. There is only one current name that i can change, and i can do it as much as i like. I also notice that while playing certain games, people will refer to me as whatever my steam name is set for at the time. Eg My friend set his steam name to Hugh Janus for a bit while playing smite and people would lol with him about it in chat. It's my understanding that you have an account name, steam name, and profile ID/URL. The account name is the one you use to log into steam and can only ever be seen by you. The steam name is the one everyone can see in your profile, when you make you posts/comments, and i believe it's also your in-game name for games that dont make you choose an account name when you start playing. Your profile ID/URL is just a name/number displayed in your profile link. I'm pretty sure that your in game now just changes with your profile names. Whether this will be the same for Destiny remains to be seen and it would be nice to have it cleared up. I hope that we either get to keep all our current names when we make the switch, or that we can just change at will. It's my guess though, that the first time we log into Destiny via Steam we will have to create an account or choose a name of some sorts. Maybe even something as simple as link our Bungie account. Who knows... i'd like to know the answer to this too though