I know I am VERY late to the party on this thread, but the discussion was interesting to read. I few thoughts I had while reading:
If the man with Dany isn't really Willem Darry, then where is he? We have no reports of his death, and if he was in Westeros, someone would no doubt recognize him at some point.
It has also lead me to think that if Dany is a fake, then who we think of Viserys was more than likely a fake as well. Two children who conveniently look enough like Targaryen's to pass for them. Except whom ever Dany see's in her vision that she thinks is Rhaegar seems to look a lot like the person she thinks of as Viserys. So, that isn't very consistently inconsistent either! However, if Viserys isn't really Viserys, then that put's Gerald Dayne right back on my radar as possibly the real Viserys!
I am actually liking the idea that Haldon Half-Maester could be the Maester from Dragonstone, as opposed to Maester Walys, as is more commonly theorized! But what does that indicate about Young Griff's true identity? That he is a baby born on Dragonstone? Whom are his parents?
Their father understood as well. "You want no pup for yourself, Jon?" he asked softly.