They could indeed, They could also land on the WCML at Willisden Junction in the former platform space that has closed, keeping a grade separated connection with the WCML, I'm still into two minds as to if a connection to the NLL / WLL would be benifical or not, I'm thinking linking in the DC Lines would be, from Willisden North, with the Willsden - Euston service being cut to a shuttle between the two? Or sent through Camden Road onwards to St Pancras or Stratford (If we need to free up HS2 space at Euston), with the majority of DC services running onto XR, can't decide if there should be XR platforms at Willisden for the Slows as well as the DCs or not. Suppose that would depend on if SN services will gain platforms in the OOC / Willisden complex, if they do, it would be worth having XR platforms on the slows as well, one massive HS2 interchange with err...
HS2, Crossrail, GWML, WCML, NLL, WLL, SN Services to E Croydon & Clapham Jcn, (hell, extend these to Gatwick!)
If you wanted to be really adventerous you could:
Divert some of the Met line or Chiltern onto it using the Dudden Hill Line and a new viaduct. (Alyesbury Route)
Run via Greenford (with new platforms) and on to High Wycome (Junction and line already there)
Link in with Thameslink, maybe some through services to the North from Crossrail (to connect in with HS2 better, or take some pressure off the Thameslink core for outer services if more ECML services get sent via TL)
So in Nym's Fantasy Land, when XR is running at 32tph Core:
From Paddington:
4tph Reading, 4tph Maidenhead / Slough, 4tph Heathrow, 4tph Princes Risborough, 4tph Aylesbury Vale Parkway, 4tph Watford DC Lines from Willisden, 4tph Tring / Milton Keynes Central, 4tph Bedford via Luton & Dudden Hill Semi Fast.
From Liverpool Street:
12tph Shenfeild, 12tph Abbey Wood, hell, make it 18tph Shenfeild, theres that many extra on peak anyway, off peak you can drop to 24tph core, and loose some of the tph up the Chiltern and Thameslink (2tph each from Chiltern Lines, all of the Thameslink route services)
(I'd like to see that route map!)