Perhaps on the other hand they'll just build the layout shown in the Wessex route study? P4,P5,P6 being down platforms, routed to down fast, down slow and down Portsmouth respectively, and the up flyover route coming down in the gap between the up slow and up fast.
I was replying to
HarleyDavidson's suggestion that a fly over was flawed, to which I would be mindful to agree with.
Personally I would prefer to have 2 up, 2 down and 1 bi directional platform, as it would allow flexibility especially in the peaks when you could have more trains heading in one direction than the other.
Even with 4tph Portsmouth services, 2tph being the Woking stoppers being extended to Guildford, 2tph Guildford to Heathrow (possibly Paddington) that would still leave 7.5 minutes between services towards Guildford on Platform 6. Whilst platform 5 would have 6tph (2 Alton, 2 Basingstoke stoppers and 2 Basingstoke/Heathrow). Likewise platform 4 would also have about 6tph.
Compare that with platforms 1 and 2 which would have 10tph each. Then if we assume an extra 8tph following Crossrail 2 then they would be at 14tph each whilst platforms 4, 5 & 6 would have no more than 10tph each.
Although reversing direction eats capacity, setting each of the outer platforms to 12tph or 13tph means that platform 4 only needs to cope with 4tph or 2tph each way (8tph would be 7.5 minutes so just enough time for a train to enter and leave the station before one heading the other way needs a slot, although it would be better if you could do 2 trains up followed by 1 train down followed by 1 train up followed by 2 trains down) and so could have some scope to help out the outer platforms during times of disruption or busy periods within the timetable.