It can never hurt to sign up for the Amazon alerts to pre-order. But being an Amazon junkie and having done this before, I can tell you truthfully that: a) I have signed up for alerts to pre-order books more then a year before they actually come out (so this is no indication of how soon Book 7 will be available), and b) I've noticed the item on pre-order days before they actually send me the alert.

In other words, I have a feeling we will not need these alerts. We'll know when pre-orders start long before the alerts reach us.