To paraphrase Steve, I won't know if I want it until I see it.
In an abstract sense, foldables seem a bit impractical to me. I've had my share of flip phones - there was a benefit to folding in order to cover the physical keyboard (avoid pocket dialing) and prevent display breakage (back before the days of super-tough glass formulations), but it also added an additional step - unfolding - before every use and every so often they accidentally folded during use.
Before the flip phone I had much bulkier, non-folding cell phones - the flip phones were no thicker than the non-folding phones. Overall they were smaller than their predecessors in all dimensions. However, a folding "slab phone" would trade off smaller dimension in one vector with greater dimension in another. I'm not sure of the benefit when it comes to an iPhone-sized device.
However, an iPad mini that fits in a pocket at all (approx. 5.5" x 4" x 0.6") might be attractive. Still, comparing the 4" width of this supposed device to the 3.07" width of a 12 Pro Max - it could be a very tight fit in my jeans.
I'm also concerned about long-term durability. It's certainly not impossible to achieve, but anytime additional flexure is added to the engineering mix the challenges increase.