Adam... Deleting SQRL identities is not in the UI and it never will be in any SQRL client that GRC endorses. This is QUITE deliberate. Those of us who have been experimenting with SQRL have been creating identities with abandon. And they have been inherently throwaway identities. But that will not -- probably ever -- be the case for real users of SQRL. I'm a bit alarmed that the other SQRL clients offer identity creation after an identity already exists as readily as they do. I think that's a mistake. I feel strongly that the SQRL UI should be designed to encourage the behavior that we want. Creating more than one identity is not something we want. Deleting an identity is almost never something that we want. So deletion is completely missing from the SQRL UI by design.
So I was actually thinking about your response as I was going to sleep tonight, and actually got out of bed to write this post before I forgot the thoughts I was having

(and so I could go to sleep faster)
I agree with you that we as testers are the edge case and the average user will only have 1 identity. But as my mind wandered I came up with a few scenarios where a delete identity might be beneficial and where someone might want to use it. I'll just list the 3 I came up with
1) Someone has a used computer that they want to give to a friend. Most people that I've seen never format a drive, heck they don't even uninstall stuff. What they will do is take personal info they have off the machine before they give it away (and some won't even do that). Now let's assume SQRL is a success and everyone has an identity. This person's identity is on this machine in SQRL but they want to give it away so they would like to delete their identity off the machine first (useless without the password I know). I will admit in this scenario if they happen to nuke the contents of the documents directory the identity would be deleted.
2) A Boyfriend and GF or Husband and Wife share a computer and they both have their identities in the computer. They break up or get a divorce. Someone keeps the laptop and the other person wants to delete their identity off the laptop, plus the other person who kept the laptop would prefer not to see the ex's name on the identity list for the rest of his life.
3) An entire family all have identities on the family computer. Now one or all of the children move out and no longer want their identity on that machine.
Obviously deleting an identity would not be click delete and "Bloop" it's gone. It would be an "are you sure you want to do this, You type yes.". and then to make sure you are really really sure, you have to type your password.
I do get where you are coming from, as we would prefer a person create one identity and stick with it rather than creating a bunch because they know they can delete the ones they don't want. You are correct, there would be those people. But there are other people who have could have a legitimate reason to want to delete an identity off a machine
With that, good night
waves 