Everything will effectively get 2 or 3 stops added so the frequencies and some stations will see increases in service level compared to today. This will enable the tph on key sections to be increased (typically +2tph compared to today).
For example the plan appears to be that everything will stop at MK.
110 or 115mph means much smaller crumple zones and far more passenger space per unit...
Post a service rejig and HS2 phase 2 in some form expect a few current Avanti paths going to more local operators as the residual fast WCML services are consolidated slightly (with more stops) won't have major city-to-city loads which have transferred to HS2. The WCML will become much more arround town-to-town or town-to-city than major city-to-city flows
Right now the WCML and ECML fast lines see two categories of traffic, those travelling relatively long distance to the likes of Birmingham, Manchester, Leeds, Newcastle and Scotland, and then those that use the lines in preference to stopping services to places like Milton Keynes and Peterborough, possibly to then connect with other services of course. Remove one and there is much more space for the others. I imagine there will probably still be through services to further afield but they may be reduced in frequency, e.g. perhaps only 1tph to Glasgow on the WCML and 1tph to Edinburgh on the ECML. With a bit of thought put into it, locations further north should still be able to get the same service level they do now (e.g. north of York/Preston) but some of those services would start halfway up the country rather than have to occupy valuable paths from London. This then allows more capacity for local/commuter services in the South, as well as providing more redundancy for those making long-distance journeys. More relevant to this thread, it potentially allows more room for open access operators to provide direct services to places not conveniently served via HS2, e.g. the Grand Central service.
Unfortunately though, yes, those travelling from quite near London but not London itself, are likely to gain from short-distance services but lose out with longer-distance services in the form of direct trains.