May have missed this already but will the new stations need to be quite large or will a simple, two platformer, small station building do (which is obviously fully accessible)?
I imagine Old Oak will need to be quite big given the interchange. I am not sure about Neasden and Harlesden - will these two need to be upgraded to handle interchange and will the interchange be OSI or within the actual premises?
I do find it interesting that if the proposals go ahead, you now have the Met line skipping two big interchange possibilities, Neasden and West Hampstead. I wonder if the Met platforms and upgrades will be made to allow full stopping of the Met now that the area is re-signalled. I have always thought WH should be the call for the Met instead of Finchley Road, but this would entail alot of work. Obviously you cannot replace Wembley Park as a call on the Met.
Then there's the Chiltern lines, but this is really another conversation and off topic entirely.