You just need to look at the Birmingham to Glasgow services to see that running between 2 major cities without going to London can be viable. Yes there isn't going to be the need for the number of IC services that there currently are, but then there is still likely to be the need for some.
And where are these major cities in the ECML corridor?
There really isn't any major conurbation that can generate large numbers of 'non' London journeys south of York on the ECML.
For instance, although it maybe quicker to run York to London via HS2, however there comes a point not that far south of York where a direct train to London will be faster than changing at York (or at least so marginal in time differance that it's hardly makes a difference to most people) such a point would change depending on how close the timetabling got the change time at York. Likewise there will be those who would rather just get on a train and stay on it until London, yes it'll take longer and yes it would proberbly cost more*, but there will still be people who do it.
I was suggesting that a break at York was likely for this very reason.
There will be still be a clockface 'all EC' stations service from London to York but it is probably unreasonable to suggest that this will continue any further north simply because the destinations south of York on the ECML (Doncaster, Newark, Grantham and Peterborough chief among them) can't really justify the through custom for anything more than a connection onto the HS2 classic services at York (or onto TPE/XC as the situation requires)
As a Scot who uses the ECML to get from Sheffield to get back north of the border, there's plenty of |intermediate" demand.
And if there's a good chunk of such demand today then there's going to be a lot more in twenty years time (when HS2 is going to be completed as far as Leeds/ Wigan).
Yes, and Sheffield to Scotland services will continue as they do now, in the form of XC trains.
The only load centres sufficient to justify cross border traffic are served by XC, not by East Coast. (I understand the Leeds-Scotland HSTs have been discontinued now?).
The 'through' ECML services will simply cease to exist and be replaced by two or probably three interconnecting short-distance services with break points at York and Newcastle as those are the logical places to break such services.
There's still slow services from London to Birmingham or London to Peterborough, despite the Intercity alternative, due to the intermediate demand. Similarly, I expect there'll be some service from London to Manchester, Sheffield, Leeds, Newcastle etc post HS2.
Yes, but there aren't slow trains from London-Preston are there?
There will still be conventional trains to York to serve places south of there, probably also to Leeds, but they won't continue on as they do now as HS2 will have ripped the supporting London through market out of them.
True, but there'll be people who want to travel between Newcastle and York or Doncaster, and there'll be people who want to travel from Doncaster to London. If you can run them all as a through service, you increase the number journey opportunities.
In Recent years the trend has to be to break up such long through journeys rather than to join them up for reasons of ensuring 'reliability'.
I see no reason why the ECML mainline services will be treated differently.
May I ask, do you have the data to support the first paragraph?
I should have clarified. Number of people who want to travel between Edinburgh and
EC-only stations south of Newcastle will be tiny.
Since that basically means Doncaster (to a degree) and points south, which can be derived by a simple demographic model showing how small a population that is.
XC and TPE will be able to handle the other through traffic with ease.
Second, I hope you do not mind me pointing this out but your spelling checker probably has a false entry in the personal override section. It's 'likelihood', not 'likelyhood'.
Actually I didn't use a spell checker

I apologise for the error in my touch-typing.