One of these days
Definition 1 of 2
Pro Tip 1/3Non-specific Future
Indicates a future event without giving a precise time. 
I'll visit Paris one of these days, when I get vacation time.
Pro Tip 2/3Casual Intent
Shows casual or informal intention, often used among friends. 
Let's catch up one of these days over coffee.
Pro Tip 3/3Optimistic Tone
Expresses hope or optimism regarding the future. 
One of these days, we'll look back at this and laugh.