When Crossrail will be open "it will be immediately full"

I read somewhere that there is a proposal to incorporate Heathrow Express into Crossrail (I don't know if that means Crossrail taking over the Heathrow Express or BAA acquiring their own Crossrail Trains to run in the Crossrail Tunnels).

Also there is another proposal to connect the WCML slow tracks to the Crossrail Tracks at Old Oak Common. This will then mean that the Milton Keynes to Euston commuter service could be diverted onto Crossrail (This maybe necessary if HS2 goes ahead).