It is my recollection that the electrification of these routes was the consequence of pro-active work by WYPTE based on an already hugely increased usage vs. when BR were fully "in charge" of scheduling*. Increased (and projected further increased) use gave a positive business case.
Why Skipton? It seems probable that whilst WYPTE's remit ends completely at Steeton & Silsden, in overall terms an end to the OHLE there or anywhere else intermediate would have been seen as utterly dumb. Skipton was an ideal turning point for practical and business reasons.
As to the use of 308s for a time - my recollection is that:
a) WYPTE were well enough funded and happy to pay for new units, but
b) any new stock deal required guarantees that repayments would continue for a long time.....and whilst
c) WYPTE themselves were quite happy with the arrangement and to give such an undertaking.......
d) nobody in the Government would offer any kind of guarantee that the PTEs themselves would remain in place for the long term. So......
e) the new train supplier wanted guarantees that IF (and only if) the PTE ceased to exist and was therefore unable to fulfil its own obligation, the guarantor (the Government) would do so, and
f) the Government (who were, let's remember, were not being asked for money; just a guarantee against the consequences of their own actions) refused and so.....
g) new trains were not procured.
Don't you just love politics?
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* Under BRs stewardship, pre-WYPTE, the base daytime service pattern on these routes was 1x hourly Bradford <> Ilkley and 1x per hour Leeds <> Guiseley only, with the intention that Leeds <> Ilkley traffic would connect at the desolate, unmanned and unsheltered halt that was Guiseley. One can only guess at what part of BR of the day saw Leeds traffic as being the half of this route most deserving of such inconvenience; the closure by stealth division, of course, tasked with driving usage down. Along comes WYPTE, restores regular through serves both ways, and the rest, as they say, is history.