I'm not that sure the small form factor is gone for real. I believe the target group for this size is just smaller, and therefore, new releases are rare and may appear every couple of years only.
The first generation iPhone SE was such a phone. Then there was a break, and we've seen the iPhone 12/13 mini. Now that all people who want a small phone have a 13 mini, we're seeing a break again.
And that's why I believe we'll see the next mini phone when the 13 mini becomes obsolete/stops receiving updates. I'm not sure when that might be, maybe in a couple of years? And then, I bet, we'll see a new mini phone.
If you want to look at it that way, then after the current "break," the next "mini" will be 6.1-inches.
