In my opinion VB is a great concept, pushing IR towards self propelled train-sets. However in my opinion, and this is my opinion, the existing infrastructures should have been totally revamped and upgraded before running VB services. We have seen existing trains get their schedules re-worked so as to accommodate VB trains.
A great example to supplement my point would be the case study of SECR, the HWH-CSMT route used to be one of the best in the country just a few years back, now it is far worse than SECR. Even NCR is doing much better with much more train and freight loads!