A second question about the risk of creating other blind spots: I imagine that under the current arrangement, when you turn to the left, there's a degree of sweep through a small arc before it becomes simply a view of the nearside of the truck. Would the loss of that sweep view be significant, given that you'll be concentrating primarily on the road you're entering? And what other loss of vision might there be?
Without the help of a blackboard, chalk, and a toy articulated lorry, this is a difficult one to explain!
I am thinking that the loss of sweep wouldn't be too much of a problem, given that the driver has already established that the area which is about to become "blind" has already been seen to be clear, otherwise he wouldn't be continuing with the manoeuvre.
The problem might arise when straightening up again, if someone has been stupid enough to move into the blind area while the lorry was turning. I had this exact situation one night when joining the M8 motorway in Edinburgh, from the city by-pass (A720).
Heavy traffic on a big multi-lane roundabout, and I am going right on the roundabout. Someone lets me into the queue, so I am effectively turning to my left to join the right hand lane for turning right. I couldn't straighten up in the space available before coming to a stop in the traffic, so trailer is sitting about 45 degrees to the left of the tractor unit. Nobber in car thinks he can take advantage and cut into the traffic by coming up the left side of my trailer, about 2 feet from the side of it! What he doesn't think about is how my trailer is going to move to my left as I straighten up, and is going to re-arrange the right side of his car. Luckily I checked my nearside mirrors (as always) before moving off and realised I would have to sit there until nobber realised what he had done. With swivelling mirrors I would only have been able to see him in the blind spot mirror.
Your idea might work better if the main mirror was split into two parts (it is big enough for that) with one half remaining the way it is in one position, and the other half able to swivel outwards and inwards in conjunction with the steering.
We don't want any more mirrors! There are enough distractions already, and mirrors in themselves cause blind spots. They are quite big, and you can't see through them.