Even if you did squeeze Stoke commuters onto other trains just imagine how it would look to Stoke passengers when a Pendolino breezes through the station at 125mph carrying mostly fresh air while they squeeze onto overcrowded Northern pacers (or their modern-day equivalents) for a slow journey to work.
The press would have a field day.
That's how it works in Germany, with a strict split between long distance and regional/local services (or a hefty supplement to upgrade).
Most local tickets are not valid on ICE/IC/EC services.
Local services have PTE-type fares, long distance quite different with something like demand pricing and few stops
You could argue that Stoke commuters, and a few other very favoured places, are getting a Pendolino service for a Northern fare, something that is not available, say, at Knutsford.
RE-type all-stations services in Germany are often only hourly, but are long and full to bursting.
On the WCML, the split would be (eg) VT versus LM/SN/NT.
Life would get complicated with services like TPE and XC, even Chiltern, which occupy a slot halfway between local and long distance.
BR started down this road with its business sectors, but in some ways the franchises, with DfT specification, have gone the other way with common user trains.
I think pick up/set down only has declined under privatisation.
On demand pricing, I have been entertained by the uproar about the Champions League final in Madrid, with 2 English teams involved.
That has resulted in the quadrupling of air fares and prices of hotel rooms, as that is the market supply and demand at 2-3 weeks' notice.
The best our TOCs can do is regulate the supply of Advance tickets, but demand pricing would have some benefits (some of the time).
For the example of Bolton-Gatwick, I'm wondering why Virgin should offer cheap Advances in high summer?
But they do sometimes have good First Class offers in the holidays when business travel is down.