Hey there Joe,
I think you make some good points. I agree that it doesn't seem to make sense to say that some wouldn't die if he was talking about an event that would happen in just six days! But on the other hand, there is a strong correlation between Peter's record of the transfiguration and that passage:
Matthew 16:27 "For the Son of Man will come in the glory of His Father with His angels, and then He will reward each according to his works. 28 "Assuredly, I say to you, there are some standing here who shall not taste death till they see the Son of Man coming in His kingdom." 17:1 Now after six days Jesus took Peter, James, and John his brother, led them up on a high mountain by themselves; 2 and He was transfigured before them. His face shone like the sun, and His clothes became as white as the light.See that? Peter said they saw the "power and coming" of Christ on the Mount of Transfiguration, and he said that Jesus received glory from God the Father, just like Jesus predicted.
2 Peter 1:16 For we have not followed cunningly devised fables, when we made known unto you the power and coming of our Lord Jesus Christ, but were eyewitnesses of his majesty. For he received from God the Father honour and glory, when there came such a voice to him from the excellent glory, This is my beloved Son, in whom I am well pleased. 18 And this voice which came from heaven we heard, when we were with him in the holy mount.
Therefore, I think that there is a very good case for this interpretation. The only challenge is that it doesn't make much sense for Jesus to say that some would "not taste death" before witnessing this. But it is possible that the Preterist is readin this as a time text when it was intended to imply only that something would happen in this life as opposed to the next life. I don't know ... I'd have to research it. But it seems that the evidence is in favor of the Transfiguration was intended. And I think this is confirmed by the fact that Matthew put the record of the Transfiguration immediately after Christ's prediction.