Google has recently added a pre-registering option to the Play Store. This means that, if you're very interested in an app that hasn't come up yet, you can choose the pre-register option and be notified as soon as the application has been released. According to the company, this new feature has been added as a way to help app developers increase the hype and interest into their upcoming applications. Of course, it is up to each developer to choose if they want to add the pre-register option to their app or not.
If you've ever used the Steam marketplace, than I'm sure you're already aware about the problems that come along with pre-registering/pre-ordering stuff. I mean let's be honest, there are some game creators who create videos and screenshots that look way better than the product they are about to launch just to trick people into giving them money. The good news is that this kind of things will not happen on Google Play as the pre-registering option will not bind you into purchasing anything, so you can change your mind at any given point. Basically, all this feature does, is notifying you about the availability of the respective product, so that you can download and install it as soon as possible.
As far as I could tell, the upcoming Terminator Genesis: Revolution game (based on the also yet unreleased Terminator Genesis movie) is the first app in the store to have the pre-register option available.