The WCML is perfectly adequate for that. HS2 is a vanity project for business and general passenger travel, none of which is certain or impossible on the WCML already.
"There is no available capacity without significantly impacting performance and causing a reduction in timetable resilience due to the resulting requirement for successive services to run on minimum headway"
https://www.orr.gov.uk/sites/default/files/om/wcml-capacity-...