How the layout is best adapted is the big question.Perth is listed up to the hilt, so it would be a massive shame not to adapt the layout whilst maintaining the current structure.
Initial proposals suggested what looked to be the removal of platform 3 & 4 for use as the main concourse and the existing depot for parking and main entrance, with a depot at the Friarton in the south to account for the drastic decrease in available stabling space within the remodelled station. For HML services, a new platform 8 island where the current wash yard is adjacent to 7, and a freight loop and further stabling facilities in behind.
Though this has changed a fair bit I imagine. For one, land has been purchased by Network Rail adjacent to platform 1 for potential stabling space that wasn't initially outlined, as well as mootings that the proposed Friarton depot will now be housed in Muirton.
Ultimatley the key for Perth station itself is maintaining/increasing stabling space on site where possible, while enhancing the connectivity from opposite ends of the station with more integrated infrastructure, the increase of parking facilities, and the relaying of track to the south to allow far greater speeds that currently account for at least 5 mins of the current journey times between Perth and the south. Not easy with inconveniently layed out listed structures build for 19th century standards and demands.
Anyone's guess, really.