On the issue of toilets, it is feasible and an option has already been budget priced to fit one of the trailer cars in each train with a toilet.
As for the technology on the trains - it is simple, modern, reliable and low cost to maintain. It has been proven, tried and tested over a very long period and when it does become due for replacement, it will be a standard, "off-the-shelf" electric Metro car (e.g. "S" stock) or a standard dual voltage Electric Multiple Unit.
The longer term strategy deals with the single line constraints and the section between Skelton Junction and York, which is too congested to provide for any additional trains over and above the current service levels.
The first stage would be to re-route the trains via the slow lines and into a new island platform at the west side of York station. This would unlock the capability to provide a 30" interval service over the Knaresborough to York section even with the two single line sections remaining.
172, (or any diesels for that matter) are just too slow and costly to maintain. This is a steeply graded route with closely spaced stations and some tight radii curves for which the acceleration and braking capabilities delivered by this type of Metro rolling stock are essential. D78 trains tackle the 1 in 28 climb at Bow Road every few minutes from a standing start. The route also must have something that can deal with large spikes in demand caused by any of the several event venues along the line (Headingley Cricket/Rugby - Yorkshire Show at Harrogate-York Races etc. etc.)
It is important to recognise that whilst 25kV electrification may be felt to be the best aspiration, the facts show it is highly likely to be unaffordable and will not be prioritised for Harrogate above other routes. There are many structures on the route (every major structure is Grade II listed) including Bramhope tunnel and four major viaducts plus many overbridges that would require reconstruction for 25kV and overhead electrification will not represent good value for passengers or taxpayers.
Remember that passengers are ultimately expected to help pay for investment via the farebox so there is a duty to ensure everything represents the best achievable value for money.
There will also be no suitable 25kV rolling stock available until 2018-20 and even then that rolling stock is OLDER than the D78's and in all respects less suitable.
On this route, many of the stations have an average distance already of around 1.6 miles between them, where lighterweight Metro rolling stock is more suited to the need for excellent acceleration and braking. If the aspirational new stations are built then the average distance between them falls even further D78 trains are nimbler than 25kV trains with shorter station dwell times so journey times are improved even more. They are lower cost to operate and 100 mph 25kV systems represent an unnecessary overspecification and costly way of improving the corridor, which has a maximum line speed of 65 mph.
The passenger accommodation on D78 trains is SUPERIOR to that generally experienced on the Harrogate line. The seats are wider, most have armrests with considerably more leg room and there is a mix of seating types providing over 40% MORE seats than is provided per train on overage. In addition to this the trains can accommodate around 700 passengers comfortably when standing is taken into account. Standing for 4 minutes on a short-hop journey from Burley Park to Leeds when the Cricket is on is far preferable than being unable to board the train at all.
The availability of this rolling stock means that all of the current constraints adversely affecting the line can be unlocked - new stations, more seats, more frequent trains, faster journey times, quiter reliable trains, lower operating costs.
Most new main-line EMU's in the UK are already dual voltage - so if fitted with the modern under-running current collection gear could use the route in the future.
The modern state-of-the art-underrunning DC contact systems are less susceptible to problems than any other electrification system - unaffected by wind, ice or snow. The system works very well in Copenhagen which has very cold icy and snowy winters - so the basic electrification is most definitely the way forward.