I agree entirely with your sentiment. I have removed identifying references from posts I can edit.
It's one of the worst-kept 'secrets' locally so I wouldn't worry too much!!! I've only just found this thread by chance, hope I can add a bit of local knowledge to the situation.
MarkyT, I looked at a similar idea as part of a dissertation-style piece I wrote on the issue, although I simply looked at adding an 'up' platform to ease some congestion between Northallerton High Jn and the slow lines. NR would never fund something like this as it would involve huge earthworks and the new bridge (already mentioned) over Boroughbridge Road, and the diversion of a farm access track, which would in turn encroach on NYCC's headquarters!
The down chord you suggest simply wouldn't fit, there's no room there are all now the site has been built on and it fills the plot of land entirely.
The idea of Wensleydale joining into a low level station adjacent to the old dairy site is not something I look at, but this would certainly work as it utilises parts of the old trackbed as well as avoiding the need to work around the ECML, its OLE etc etc.
As part of my project I modelled the situation, I only had accurate date for passenger trains at this point (I now have freight data and may develop another, more accurate scenario using this) and the impact would be minimal. It would remove the conflicts at Northallerton High Jn, but new paths would be minimal, as the line is already only double track to Darlington. I'm not sure how valid my methodology is but you might get an extra couple of paths in each direction per hour (largely guesswork!).
But surely, to reduce delays caused by conflicts at the junction this idea would have some milage?!