Why would it be a passenger service? The very nature of it tells you it wouldnt be. It will be to test stepping distances, station operations, running times etc....
Going off topic, but do you reckon we'll ever be able to just "model" such runs, without having to run a "Route Proving Run" service?
Given that we surely know the dimensions/envelope of the Voyager and what trains already fit along the line to Shrewsbury, I wonder whether one day we'll be able to trust that one would fit (e.g. if a 23.71m 175 coach* can fit then do we need to find a spare Voyager/ find a spare path/ find spare crew to test the clearances? can't we trust the timings that 175s cope with?)
Does the Network Rail New Measurement Train not provide all of the answers?
(obviously there'll need to be driver training etc done, it just seems like quite an expensive/ complicated/ time consuming exercise to go for in the modern age)
* - figure taken from Wiki, I appreciate that 23.62m long 170s and 23.2m 153/158s are more regular on that route than a 175, and that the extra fourteen centimetres between a Voyager coach and a 175 coach will have to be taken in to account, but this is more of a general question about whether computer simulations will one day be enough to certify route clearance etc