What exactly are you referring to when you ask about "typekey implementation"?
TypeKey is up and running quite successfully. Unless I'm missing something, everything you're asking about is working - you may just not have set up correctly, especially if you're using your old templates and have not adapted them for 3.0D. It's not about the code used to display the comments (like SimpleComments does), but how the comment is submitted, the forms used, sign-in links provided.
If you want to find out how it all works, I would suggest you take a look at the
default templates, specifically the Individual Entry, Comment Listing, Commemt Preview, etc templates, and check out the new template code that is required. Create a new blog with the default templates, even, and enable Registered comments, and do some testing. Searching the forum will undoubtedly offer you even more information.
And I believe the tag
hipnerd intended to refer to was MTCommentFields, not MTSimpleComments, which is a plugin tag.