Full electrification is looking inevitable - the benefits of four tracking are only fully realisable if there's a switch to higher performance electric rolling stock which will give the desired acceleration and headway performance being sought. Four tracking, on its own, risks slowing down services as additional station calls can be (re)introduced, particularly if they are slow accelerating diesel units.
And presumably similar arguments can be made for the section between Neville Hill and Church Fenton. Faster accelerating EMUs will help ease the capacity crunch on that section. The argument is perhaps not as strong as that for Huddersfield - Leeds but still, should be enough to tip the balance you'd have thought?