It might be worth keeping an eye on TypeKey to see if it can be used to allow authenticated comments from non-LiveJournal users later on. I'm a bit wary of using a centralised service like this, but if it becomes popular with weblog users other than those with MovableType it might be good to offer it as an alternative to other login systems that have been discussed in this community in the past.
They're keeping quiet about how it works for now, although I've seen it in use on a few different weblogs recently, so it appears that the service is active.
