Has always puzzled me this one as a Reading MK service, whilst always planned, is going to cause some lovely conflicts at Oxford in the down direction as it is going to have to cross the job. Especially if the plan to make the middle roads the freight loops goes forward.
Have been pondering this point as well. However, given that while the future of Oxford station and the wider Oxford area is up for discussion (there is a rail industry/city and council councils working group looking at it) at the moment, anything could happen - perhaps with reordering of the tracks to be paired by purpose (like Paddington to Didcot) rather than direction of travel.
You, I'm sure, will know rather better than me if it would be a better idea to sort trains out on to such a formation at Wolvercot junction and Radley (the outer extremities of the existing four-track formation available in the Oxford area, though there are only two or three tracks on much of it at present), rather than near the station.
The theoretical Oxford station layout included in the GW route utilisation strategy
http://www.networkrail.co.uk/browse...trategies/great western/great western rus.pdf (page 248) a couple of years ago showed a twin-island layout with two through roads for freight.
There is information somewhere in the mountain of Evergreen3 paperwork that says the proposed Chiltern bay platforms at the north end of the station are designed and aligned to form part of any future through island platform at the eastern side of the station (the existing main building would be demolished).
If the lines through the station were to be paired by purpose, rather than direction, then you could potentially minimise conflicting moves at Oxford North junction by having Marylebone/East-West trains using the eastern island (and moving straight off on to the proposed segregated through line past the stabling sidings) and GW main line and XC services on the western one.
I'd admit though, that pairing in a fast lines/relief lines fashion may not make best use of the freight through lines.
But I can't see a flyover at Oxford North ever getting off the (rather soggy) ground, so some other approach will probably be needed.