I hope First-Trenitalia can introduce good services once HS2 is complete, there are already planned services on Wikipedia ( I know), and these don't look too great. Firstly I might be missing something but im struggling to see why every single service should stop at Old Oak common, for example I doubt many people coming from north of Crewe would interchange there. Secondly, a lot more services will start/terminate at intermediate stations on the WCML, meaning there are less London services.
For example, at Warrington, there will be 3TPH to Scotland (2 to Glasgow, 1 to Edinburgh), however, there will be 1TPH to London. That means there will be more trains heading for Birmingham than there are to London. Wigan also suffers this, although Wigan receives services to Manchester interchange, despite only having 200,000 more passengers than Warrington, it receives DOUBLE the amount of services per hour, along with all of the Northern and TPE services.
I hope that, being Wikipedia this info is all nonsense, and that I can take it by a pinch of salt, but if it is then they need to revise it.