He says this:
Additional information or restrictions are needed to maintain consistency.
I both agree and disagree. An additional restriction would make it easier for the user to know how to use the format. However, since it's the theme itself that's interpreting what the format means, the theme designer should be the one who's creating those restrictions and explaining them to the user. It doesn't make sense to add this sort of thing to core until a clear standard on how themes are using these formats emerges.
Realistically, I'd prefer it if my theme had no restrictions and simply interpreted the post the way I want it to be interpreted. That is to say that the theme should be smart enough to figure out what I mean. If I make a "link" post, and I put in text with a link in it, then the theme should figure it out. If I only put a URL in, then it should figure that out too. Making the user fill in some preset form is worse than making the code smart enough to know what I want. Putting the complication back on the user to fill in the form correctly is lazy programming.
Also, the theme is perfectly capable of inserting javascript onto the Edit Post page and thus changing the form around when the format is changed. Ideally, such a system wouldn't use any postmeta fields, since they probably wouldn't be necessary.