I'm not convinced that those ultra-long routes are worthwhile – the longer the route, the more complicated it becomes to timetable, schedule and operate robustly and reliably. You end up with buses running a long way from their home depot, which makes it vulnerable in the event of breakdowns or other problems. It's harder to vary frequency or capacity on different sections of the route to meet demand appropriately.
Very long routes tend to work well in two circumstances: (1) where they fill a significant gap in the rail network connecting substantial towns with no useful rail link, and (b) links from sizeable urban areas to the seaside. Those are the times when people will be prepared to sit on a bus for a long journey ... and if you haven't got through passengers then you haven't got a rationale for a through service.
In North Yorkshire, the X93/X94 and Coastliner meet those goals, but not the routes you've suggested.
- York – Northallerton – Darlington is a corridor that is well served by rail. There is strong demand for buses between York, Easingwold and Thirsk, but not beyond that. Northallerton to York is at least every half-hour by train, with journeys taking 20–30 minutes, whereas by bus you would be looking at 90 minutes. From York to Darlington, it's even worse. Demand for travel from any other intermediate villages is minimal.
- York – Helmsley – Scarborough is a long way round for no good reason. It would take about an hour longer from York to Scarborough than the direct 843, and probably 45 minutes longer from York to Pickering than the direct 840. Demand for travel from Easingwold to Pickering and Scarborough (and other intermediate villages along those two corridors) is negligible.
- Ripon – Northallerton – Middlesbrough is not serving any viable market long-distance. It just isn't.
- Leyburn – Northallerton has been done to death already but isn't an ultra-long route anyway.
That isn't to say that I think all the bus services along those corridors are adequate and are not in need of improvement – but that the improvements need to be localised and tailored to what potential market there is. For example, I do believe that the Scarborough to Helmsley corridor merits an hourly service ... but I can't see the need for that frequency between Helmsley and York, increasing that to every 2 hours would be ample. That's why linking them together isn't the right solution, because demand is going to vary significantly at different points along the route.