A four platform station between Euston and St Pancras with the tracks continuing onto HS1 and a large set of stabling/storage/cleaning etc sidings at Ripple Lane.The problem is that there's nowhere logical to send them. Long distance trains run through Birmingham because there is, but London is in the bottom right hand corner with no major intercity destinations to the south and east.
Then trains would go out of service at the new station and run ECS to Ripple Lane. You would also have the option to keep some in service to Stratford or if you wanted to be really bold run a few beyond there to Ashford (and maybe even one or two to Paris etc).
Not going to happen though