Well, I'm the aforementioned bfiggins. Minkahar's origins are pretty simple: I got excited about LEB, opened up the character builder, and looked through my options, looking for something new I haven't tried yet.
"Hmm, Kalashtar. They're big in Eberron, aren't they? Let's see what class works well with them...ah, they make great Ardents! Let's do that."
I never really gave a thought to approved sources or not, and so I missed the PHB3 ruling.
That being said, I'm in favor of allowing the debut material for the PHB3, and future materials. Wizards said it themselves (quoted in full earlier in this thread) - this is not playtest or preview material, these are pages directly from the book itself. My impression is that Wizards considers these classes/rules a bonus for D&DI subscribers, and that they encourage them to be used just the same as any other book.
It's true that there may be errors, and those errors may take a long time to fix...but that was even more true of earlier physical books. Double weapons, battleragers and the like.
For me, it's not really a big deal - it's true that I'm interested in playing a Kalashtar Ardent, but it took me all of ten minutes to re-spec him as a Warlord. I just think it's important that we understand the purpose of 'debut' material - is it playtest, or is it release?
Fortunately, this is a question that will resolve itself in a few weeks - as soon as we have the PHB3 in hand, we can check for ourselves to see if everything is exactly identical. It might be most productive for me to just roll a Warlord for a few weeks, then we can return to this discussion when we have some new evidence.
(Also, I don't remember if/how they noted the updates to the Monk and the Hybrid rules in the CB. I seem to remember them being clearly marked as Dragon playtest articles in the CB...a distinction which doesn't isn't there now.)
One final note: If possible, LEB should definitely provide a downloadable .dndcamp file which marks which books are used, and which aren't allowed yet. With that file, players with the Character Builder can just import the campaign, then build their character however they want, knowing that they won't accidentally use any disallowed sources.