This is also what I was thinking everyone was talking about - TKD/Karate style side-stance...guess I was wrong as well.
On topic: When only hands are involved it's natural to want to turn a little to protect your mid-section, extend that lead arm for range/distance and also load the rear for power. It's a viable strategy and I've sparred guys who do it effectively in boxing-only settings but there's always a trade-off. By extending that lead arm you get more range but you also reduce it's power, and you also reduce the speed of the rear straight since it's farther away. The basic 1-2 and 1-2-3 can't be peppered in during exchanges as quickly when you're sideways as when you square up IMO.
The big question here is - how does it affect your sprawl? If you can't sprawl as effectively it's definitely a risk you might not want to take considering the weight of top-position in modern MMA judging.
The thread is about standing like how Rory Macdonald stands, as specified in the OP. And even in the picture provided in the OP his lead foot is turned in a little more than normal. He has easily the fastest right straight in his division, matched only by Kampmann.
Rory also has zero trouble sprawling.