Tom Anderson wrote:
And there's quite a few more trains west of Paddington planned, which
would require platforms Paddington doesn't have.

Okay, i thought it was path-for-path. There will be more actual trains
under Crossrail?

There have to be. Extending the line makes the existing line desirable to
more punters - if it didn't, there would be little point in extending the
line in question.