I have seen a few scott-T's but never that.
I would be interested in a example.
Well, this is an example from the theoretical side, I have no idea if anyone does this.
@winnie has described this idea before:
Say you have a 150 kW 3-phase supply, and all your loads are 120/240V (so 120V 2-wire, 240V 2-wire, and 120V/240V 3-wire). If you're OK with 120/208V "single phase" 3-wire on the secondary, you can just use a 150 kW 3-phase transformer with a 208Y/120V secondary (or maybe your supply is already 208Y/120V and you don't need a transformer). But maybe for some reason you insist on 240V L-L on the secondary, not 208V L-L.
Then you can use (3) 50 kW 2-wire primary, 120/240V 3 wire secondary transformers, with the primaries arranged A-B, B-C, and C-A. You get (3) different 50 kW 120/240V supplies you can distribute your loads amongst. Because the neutral point of each secondary is grounded, the voltage phasor diagram of all 3 secondaries together looks like the 6 lines from the center of a hexagon to its 6 vertices. Hence the name hexaphase. But if any given load is only supplied by one individual transformer, that relationship between the transformer secondaries is academic, the loads don't care.
I took your earlier comment to suggest you could instead use a Scott-T transformer to get 240V/120V 2-phase. That can't possibly use the 3 phase supply as efficiently. While one of the secondary L-L voltages is in phase with one of the primary L-L voltages, the other secondary L-L voltage is at 90 degrees to that first secondary L-L voltage. So I believe the current on this second secondary L-L leg will end up split between the two other primary L-L voltages. Then, for example, if the load is resistive, the current will be out of phase with both of those two other primary L-L voltages, and your available Watts on the secondary will be less than the VA of the transformer. [I need to look more closely at the Scott-T transformer diagram, but I believe this should be similar to supplying a 208V load L-N on the a 240V high leg delta secondary.]
Cheers, Wayne