Watch this space
Definition 1 of 1
Pro Tip 1/3Expectation Building
Indicates something interesting will happen, building anticipation for the future. 
Our new product line will revolutionize the market - watch this space!
Pro Tip 2/3Informal Use
Commonly used in casual or informal situations like conversations or social media. 
I'm working on a secret project. Watch this space for the big reveal!
Pro Tip 3/3Not Immediate
Suggests the news or event will happen later, not right away. 
I've just started writing my novel. Watch this space for updates in the coming months!