I'm hoping you meant
east of Cross Gates
Looking at Google Maps, the boundary (and the viaduct over Selby Road) look capable of still taking four tracks but we don't know what the ground conditions are on the embankments. Heading further east it's still four-trackable, and I'd like to think that the new East Leeds Orbital Road just east of where Thorpe Park Station will probably be has a bridge with a large enough span... though it doesn't look like it to me.
I'm with
@Neptune on shuffling Garforth 200m eastwards and closing East Garforth, but realistically it's going to be tought having four tracks east of Thorpe Park to Micklefield. Might four tracks between Leeds/Marsh Lane/Neville Hill and Thorpe Park be enough to allow fast trains to overtake stoppers?
The other question is how to pair them; west of Leeds/Dewsbury they are by speed whereas Cross Gates was built with by direction in mind. No reason they have to be the same, of course