Having said that about the empty space around Basingstoke station, it occurred to me that I don't have (and can't find) any recent maps or images to check for encroachments. But I can think of two I've heard about - the ROC just to the north and Basingstoke Campus on the junction triangle.
The relatively new signal building (known as Basingstoke New) alongside P5 (so immediately north of the station) is only temporary, it will all be moved into the ROC in due course. The future ROC is the main function contained in the Basingstoke Campus, the training etc is the sideline. The Campus is well away from any track.
But I think NR are trying to do far too much in the station area with the proposals in the Wessex route study. I suggest they would be far better running the pair of Reading lines west of the station through two full length platforms, and sorting out the grade separation of the down line of that pair somewhere between Basingstoke and Working Jn. There's no real need for it to be at or near the existing flyover - doing it further east may allow it to descend between the two existing down lines which would possibly be more flexible. The up line would just be a normal junction off the existing up slow.
If they still want a bay for Reading stoppers, then move it onto the other side of the existing platform. Then the existing bay becomes P6, and a new up line towards Reading a P7. Then leave the existing junction alone for reversionary routes during maintenance.