I would love an Epic Book to be handled by Paizo(the original needs to be rewritten so badly) , the idea of having classes over 20th level was the best D&D supplement ever done, I know I'm not the first to say this but im sure I'm the first to say this; don't bother with a subscription, if i want a rulebook or supplement I will buy it!
Lastly although a few prestige classes are good I do think placing them in a book is a waste of space that could be used for more important material. your onto a winner though because 4th edition D&D just turned it into a card game.... horendous!