Wow, if true then Pentax/Hoya wants to make a statement here. Is Pentax on the way back? Either way, I find the DA* 400mm f/4 believable because I think they want to keep the longer lenses in the same "family". Why a DA* 200/2.8 and DA* 300/4 and suddenly a DFA* 400/4? So this is a perfectly plausible explanation to have it under the DA* family.
And about the DFA* 50/1.0: that would be quite an engineering feat and likely to be impossible. Unless there are new glass types and/or optical solutions to make lenses faster even with smaller bayonets? Not impossible with Hoya (most important glass maker) as the mother company...
Talk about putting Pentax back on the map...