I’m in exactly the same boat. Now that a Mini is a powerhouse and can be replaced more easily and cheaply than an iMac with an integrated display, I’m going to replace my 27" with a mini (or a studio) and a nice large display.

I’d like to pair it with the Apple display, but it’s outrageously expensive, and the newly released Samsung studio display (ViewFinity S9) might be a reasonable option.