Just a discussion starter really, as in the thread title. Some personal opinions:
Northern England
Alnmouth-Alnwick - Possible, and the Morpeth services could be extended to terminate there as well
Seahouses-Chathill - Doubtful.*
Bishop Auckland-Penrith via Kirkby Stephen - Long way round, surely? If your going to head that way, then Preston would be a better idea.*
Skipton-Colne - Needs doing as a priority [1]
York-Bridlington - No chance. York - Hull via Beverly however ....
Menston-Otley. Where would it go after Otley?
Harrogate-Northallerton via Ripon - Good idea.
Durham Elvet-Pelaw/Sunderland (as part of TW Metro). Nope, not as Metro
Nunthorpe-Guisborough Not a bad idea actually. It could even be extended to Redcar and make it an hourly circular service.
Battersby-Picton (plus new southern chord for Northallerton) No chance. Seeing as Picton is next to the Northallerton - Middlesboro line, just build a station there.
Knottingley-Doncaster (Askern line). I thought this line was still open?
Low Moor-Horbury Bridge via Heckmondwike
Leeds-Huddersfield via Birstall & Heckmonwike (Leeds New Line). These 2 are probably not economically viable, as there will be a lot of bulldozing required.
Darnall-Stocksbridge via Sheffield Victoria - Worth it for 1tph each way?
Sheffield Victoria-Hadfield (Woodhead route) Not worth it. Far better to invest in the Hope Valley line.
Matlock-Buxton - Needs doing as a priority [2]
Cross Gates-Harrogate via Wetherby. Not economically viable in my opinion.
Wakefield-Dearne Valley Parkway via Cudworth
Barnsley-Dearne Valley Parkway. I presume all these services going via Cudworth would to/from Sheffield. If that's the case, then it's a no-go as without a massive rebuild from the Dearne Valley to Sheffield there is very little capacity left between Swinton/Meadowhall - Sheffield
Alnmouth-Alnwick: Agreed, good northern terminus of a wired stopper for stations north of Newcastle.
Chathill-Seahouses: Would be very good for Tourism in northumberland, would provide a much better public transport link to Lindisfarne than now, and would allow commuting south
Bishop Auckland-Penrith: For serving towns & communities in the north of the Dales e.g. Castle Bolton
York-Bridlington: Don't see why not. Some good sized communities between York & Driffield e.g. Stamford Bridge, Market Weighton, Pocklington all of which would allow for good flows from Bridlington & Driffield into York.
Menston-Otley: Nowhere, simply an extension of Wharfedale line to give Otley rail services into Leeds.
Durham Elvet-Pelaw/Sunderland: Best as metro IMO, certainly if there's an upgrade. Metro would also allow for diesel running on some sections with heavy rail.
Nunthorpe-Guisborough: My thought exactly, especially with the 'Tees Valley metro' which should really work through to Hartlepool & Bishop Auckland in the west.
Battersby-Picton: Would give whitby etc connection to Northallerton (& Hence Leeds & York) without need to go via Middlesbrough, which would hasten journey times considerably.
Low Moor-Horbury Bridge: actually quite viable aside from supermarket carpark at Cleckheaton, otherwise the trackbed is unencroached.
Leeds-Huddersfield via Heckondwike: One housing estate and one tunnel clearance, but then quite easy. Huge benefits for returning direct connections to Leeds & Huddersfield for Cleckheckmondsedge as well as providing a route avoiding Morley & Dewsbury into Leeds.
Darnall-Stocksbridge via Victoria: had thought of as part of a HF Penistone/Stocksbridge-Retford/Bolsover 'Sheffield crossrail'
Victoria-Hadfield: New northern route out of Sheffield better utilises connections into Manchester, especially with increasing needs of passengers and freight.
Cross Gates-Harrogate: With Wetherby-Harrogate/Leeds commuters, definitely viable, especially as will pick up commuters from East Leeds suburbs e.g. Scholes, Thorner, Collingham (all quite well off) to carry into Leeds. Wetherby-Harrogate potentially less viable, but Wetherby-Leeds eminently so.
Lines to Dearne Valley parkway: Would be heading northbound via Royston & Barnsley into Leeds, providing connections for Stairfoot, Darfield, Cudworth, Royston & Brampton (totsl pop. approx 60k), as well as terminating near South Yorkshire's new business park area north of Rotherham. Certainly would work IMO.