Wouldn't it be relatively cheap to lengthen the platforms even
further? With the high level of overcrowding now and even more
passengers using the route in the future, it seems like it will be
needed. 8 coaches seems like a good number indeed.

Longitudinal seating is simply needed on routes like this It might be
slightly less comfortable, but that's not what peak train travellers
will be thinking about. They're just happy to be able to get on.