I want a registrar to sell domains, not be a platform for marketing other services to me. I want one registrar which will sell me any tld, many of the nice-looking registrars don't support .uk or .dk domains. I want there to be a well-documented API for setting up dns, and this may be a partnership with Zerigo. I want their website to not make me think. I want to have sub-accounts for my clients to handle their own domains, white-labeled if possible. I want one-click setups to point to Google Apps, Heroku, etc. And whilst I'll pay a premium for this, I don't want it to be so expensive I can't afford it.
This is very much the direction I am trying to go. Of course I will be releasing as early possible. But many of the things you mentioned are on my radar, except for the dns api. I'll have to check out Zerigo.
I am starting out as an Enom Reseller. It looks like I should be able to do .uk domains day one.
This is an announcement of my current project. I have a very good idea of what I want in a domain registrar, but I would love to hear what other people want. Please let me know if, if you have the time.