It's also an incredibly stupid route plan. The Western and Eastern end points are in the green belt in the middle of nowhere. The obvious extension to Crossrail would be to Reading in the West, which could potentially eliminate a fair proportion of road traffic on the M4 by providing a park and ride option to Heathrow, London and London City airport.
Instead it's going to start at Maidenhead, which may possibly pick up some of the existing commuter rail traffic, but will do next to nothing for drivers.
There are other idiocies, which deserve a diary of their own. (If I can be bothered to write one, which I probably can't.)
There was an alternative scheme which was much more imaginative, but because of the sclerotic nature of infrastructure, and especially rail in the UK, it would have meant starting the design and funding process from scratch. So - not happening.
So Crossrail is going to be hugely wasteful, providing somewhere between a third and a half of the regional throughput it could have provided if managed and planned properly.
I imagine it will extend to Reading eventually for the very reason you specify. In fact, just as Thamelink goes from Brighton to Bedford, Cross Rail will probably go from Colchester to Reading/swindon.
It's a compete waste of money that doesn't address a single strategic requirement in the South East. Biggest screaming need are decent transport links along the south side of the Thames.
Although frankly, if you were gonna throw £16 billion at any infrastructure need, I'd say a hi-speed rail link to Scotland might be useful keep to the Fen Causeway
