I think the critical issue is to attempt to understand this from a believer's perspective. I'll make my best attempt, shown below -
jon wrote:1. Joseph attempted at translation of the Kinderhook Plates
We knew that and Dons presentation doesn't change that.
But if he used the GAEL, it doesn't tell us anything about how he translated the Book of Mormon or the Book of Abraham.
2. The Kiderhook plates are forgeries
I don't think this is disputed in Dons presentation.
If Joseph recognized a symbol on them that was consistent with the GAEL/Egyptian papyri symbols, then he could be excused from initially not making this connection. That he did not complete the translation may tell us he came to suspect the forgery only as he began to match the GAEL to the rest of the plates.
3. Joseph wasn't using divine inspiration
Hardly a surprise.
Only in the sense that he wasn't attempting a pure translation of the plates. But he was drawing from his past revelations. There is a lot of speculation regarding the GAEL's meaning now, but in essence, it's use could be explained as Joseph was working a secular translation out in his mind, and the revelation came later when he realized he should stop.
Again, Don's presentation seems interesting because it gave us more information to consider. The effect is has on the arguments is tangential in that respect, but seems to require a reassessment of the old arguments on both sides.