I'm yet to come up with a full timetable, but it very much depends on what route HS2 is going to take, and how much more line speed can be teased out of the ECML between York and Newcastle by ERTMS and ETCS fitments...
I can personally see 3tph between Newcastle and Edinburgh (1XC, 1ECML and 1HS2)
I'm rather concerned whether that is sustainable, for quite a few reasons. The end-to-end traffic would inevitably gravitate towards the faster train, the HS2 working, leaving the ECML working dependent on those passengers travelling anywhere that's not London. To retain end-to-end traffic, the fares would have to be at least 25% lower to retain appeal, and that means cutting costs, so we can expect to lose on-train catering and have high-density seating. The result would mean that the ECML is perceived as the secondary line, thus pushing more passengers to HS2.
I don't really see a through ECML service to Edinburgh lasting for more than five years before it gets cut back to Newcastle and a second HS2 service goes in its place. As you can guess from where I live, I'm not too keen on the idea of losing my link to Scotland.
For Tyneside I would (personally) be developing Newcastle Central with a parkway station at either Washington or Gateshead MetroCentre, with a classic line connection East of Newcastle Central. This of course would be when dedicated infrastructure comes to reach Tyneside, simple gauge improvements can be provided to get through the suburbs of Newcastle toward Edinburgh.
From what I remember of the line through Heaton, it used to be four-track and was cut back to three. Reinstating the fourth is probably technically feasible, but realignment of the current three to accommodate wider trains is another option. Height is the difficult factor, there are several low bridges. Add a Morpeth avoider and some other tweaks, and the times should come down somewhat. At the southern end, one option would be Tyne Yard, but that still forces all traffic over the King Edward Bridge. I also like the idea of using parts of the old Newcastle-Carlisle (which crossed the Tyne at Blaydon) but that would make it harder to reach from the south.
For Tyneside, I'd be looking at sending a Classic Compatible service that way, if we have 3tph CC services running initially, with 3tph to Newcastle and 3tph splitting off for elsewhere (Ex. Leeds) there is plenty of scope there for 1tph to Middlesbrough or Sunderland. The remaining 2tph running to other places in Yorkshire and Lincolnshire (Splitting off at Sheffield or York)
This all sounds sensible. 1tph might come off HS2 at Leeds and run York-Northallerton-Darlington-Durham-Newcastle Central, another might alternate between Middlesbrough and Sunderland, with a third covering Hull, Bradford, Harrogate or somewhere else. Doncaster would lose out badly, though, unless the Hull train came off at Sheffield and ran via Doncaster. However, I'd expect Hull to be covered by an hourly semi-fast from King's Cross.
Since I'm working here on HS2b E&W reaching "Leeds Delta Junction" and "Manchester West Parkway" with a connection retained at Rugley, possibly an additional HS connection to Crewe.
On the 'classic' ECML I would look at retaining 2 or 3tph core services, but these would call at more intermediate stations, all calling at Peterborough and Doncaster, extending from here to Leeds and Newcastle, possibly 1tph per Leeds and Newcastle, with the remaining 1tph running from Doncaster to somewhere more fun...
3tph, one express to Newcastle and two semi-fasts to Leeds and York/Hull sounds like a distinct possibility. That would 'suburbanise' the southern half of the line to some extent. In some ways, it's an improvement. Retford for instance would get 4X the current service, while the Thameslink routes might see an increased frequency.
Thing is, what would it really be like? Most likely, a South-Eastern 'Javelin' service with no on-board catering, no first class, high-density seating and almost no trace of the 'Route of the
Flying Scotsman' that I used to know. Whether it remains any use to me, travelling from Hitchin to Scotland, depends on how the connections are handled. There are also political concerns. What happens to Newark if it becomes a London dormitory town? What happens to Peterborough if it loses its excellent links to the north? Will the York tourist trade be affected?
Of course, good management can avoid the route deteriorating. A best-case scenario is essentially minimal change for me and faster journeys for through passengers. I really want to see that, but I hope you see why I'm concerned.