When I read your original plan to 'create 3 long platforms' I naturally thought you meant 3 more but I see now one of your 3 would be an extended P2. Is that right?
Nonetheless I still think the width of the new island formed between P2 and the joined P1 and P9 would be a limiting factor.
Yes that is what I had meant.
Things might be tighter than would be ideal but to my eyes this would be the best fit.
It might be possible to rebuild the area on the south side, the "local" platforms, but this would probably mean the rail connection over the high level bridge would have to be abandoned and the construction work would have to take place on platforms already in use. The joining platforms one and nine option would allow much of the construction work to be done without blocking platforms in use.
I am assuming by the way that longer HS2 trains are going to be running to Newcastle
. All sorts of other issues such as the line over the High Level being taken out of use and redevelopment around the JT Dove premises might have an impact on what happens.