There were mentions in the letter columns here and there, along the lines of "Joe Casey and Grant Morrison take over the books in April", but it's not like it was "GRANT MORRISON!!!!! READ THIS!!!! ARGH!!!!"

Hyping things in the letter columns at that point in time was kind of odd. Most folks were getting their news from Wizard or the internet, and already knew about the changes coming. By the time news ever broke on a letters page, it was already common knowledge, even if it was just due to the solicitations.

But why would they need to hype Grant Morrison within the book itself? The point of getting him to write was to gain new readers (or regain those that had left). They expected the people currently reading the books to keep getting the books.