Ok, let's begin with the most important thing:
SPOILER ALERT
Ok, got that out of the way!
Seven things stand before
the entrance to the Lackless door.
One of them a ring unworn
One a word that is forsworn
One a time that must be right
One a candle without light
One a son who brings the blood
One a door that holds the flood
One a thing tight-held in keeping
Then comes that which comes with sleeping.
Now, I can't solve all of the bits to this "Riddle rhyme" heard just after Kvothe's time in Felurian, but I feel that there are some well-hidden hints and suggestions that point to this being one of the truthier stories/ songs.
To start, this door leads to the Amyr. I think the Cthaeh suggests this rather strongly when he states that the Maer is near the Amyr but knows it not. The Lackless have a door that holds SOMETHING but we don't know what. I suspect the Amyr themselves or some way TO the Amyr. The trick is opening that verisame door.
Now, as for the bits of the riddle: The most obvious of the lot, and the one that most strongly points to this being significant, is "One a son who brings the blood." Why? Because Kvothe is Edema Ruh and a Lackless/Lockless heir. The Lockless' oldest child ran off with a ravel bastard, leaving an angry and Ruh-hating sister who, as Kvothe notes, bears a striking resemblance to... to... someone. Who fits that story bit the best? Why, how about Kvothe's mother, who ran off with the Edema Ruh leaving her family behind. Further adding weight to the argument, she was particularly upset at Kvothe's song about Lady Lackless and the things hiding underneath her black dress. That makes a lot of sense now.
So, now we have a riddle about opening a door that is likely associated with the Amyr. As I said, the answers to the riddle are still a bit too vague. Could a ring unworn refer to one of the rings Kvothe eventually earns via naming? A word forsworn could be anything, perhaps a broken promise makes the best sense here. The timing could be anything, though maybe a full moon or moonless night could be significant. A candle without light... sounds like a black flame. A blue flame? Chandrian? Maybe. The son (Kvothe). A door that holds the flood.... could be the door itself, or could relate to the door deep within the Library. AND could relate to the door of stone which holds... I think it was Iox who captured the moon. Felurian mentions it, anyways, in describing the creation of Fae. A thing tight-held in keeping... that could be near anything that the opener, presumably Kvothe, holds dear. I'm going with his Lute on this one. Perhaps his music. Perhaps his power. I'm betting on music, given the frame story's significant lack of any. drop. of music. anywhere.
And lastly, comes that which comes with sleeping. DREAMING. Which leads to my ultimate theory: the framework story is a dream in which Kvothe is trapped as he attempts to free the Amyr and destroy the Chandrian. Well, the dream bit is the important part. As for Bast, I believe he represents either an outside power (Felurian?) or a portion of Kvothe's mind attempting to stir Kvothe into action through remembering how he got into the Dream. In fact, it could be said ALL of the characters are parts of Kvothe's mind. And the thrice locked chest of Kvothe the Bloodless? Not sure. I've got my money on his music, his power, or some horrible terrible memory which he has tried very, very hard to forget... but which is key to his freedom.
There are a few more details I suspect, but those are the big ones I think I can support with some evidence from the stories themselves.