I'd assume that Part 6 of the Player's Guide would come out between Adventures 2 and 3 since the 5e model for prestige classes starts them at 5th level and the Campaign Guide lists Adventure 2 as levels 4-5 and Adventure 3 as levels 6-7
I'm definitely interested to see how they turn out
I'm more interested in when the next part of "The dying skyseer" will come out, but yeah, some vague idea on what the prestige classes will be about could really spark my players imagination