I've been using Outlook.com since July, read several issues regarding the .outlook email name issue.
If you open a new account with yourusername@outlook.com it can't be merged with you existing yourusername@hotmail.com account.
I just added an Alias myusername@outlook.com to my myusername@hotmail.com account and you get the outlook.com email in your old hotmail account, when using the outlook.com interface.
Seems to be a lot of posts with people having problems with an outlook.com address, I'm sure there are other ways to accomplish this, the above method worked for me.