I'm curious about this myself. I do hope they're not building the new entrance over them, as it would be very short-sighted to build on that formation. It could be used so much better, ideas I've had in the past included a SSL link from Edgware Road or Notting Hill Gate, (rising up east of West Hampstead with a new platform on the south side) then the Wimblewares being extended up to Mill Hill, with Thameslink then running fast through Hendon, Brent Cross & Cricklewood. At a later date, the additional pair of tracks could then be extended north to St. Albans (which the Midland intended to do, but never quite got around to it before the mergers), thus removing the inner suburban services from the Thameslink tracks completely, (i.e. Thameslink would serve stations to St Albans, fast to West Hampsted, then all stations through to Blackfriars). The Wimbledon to St. Albans service would be St Albans, Radlett, Borehamwood, Mill Hill, Hendon, Brent Cross, Cricklewood, West Hampsted then either a) Kilburn High Road, Westbourne Park, Notting Hill Gate, or b) Lords, Edgware Road, then as currently. If you could somehow knock through from High Street Kensington on that route, you could have a segregated service from the Circle too.
Alternatively, a chord down from the North London line could do the same, but without the useful but expensive cross-London aspect of the plan.
I guess you could even send the Bakerloo north from Maida Vale, build a proper interchange at Kilburn High Road, then loop around to pop up east of West Hampstead and go on west from there, leaving the route west from Kilburn High Road to the Overground.
Anyway, the point is, I hope they're not building on a useful track formation.