Maybe this post does have something of a logical foundation, but is probably more late-80s or 90s than 2020s in outlook, so perhaps not nowadays. But here we go:
Once HS2 is done, use the "classic" WCML to help introduce a new and revamped Cross-Country network, with InterCity-quality bi-mode or dual-voltage trains. Interiors similar to the originals for Mk-II and Mk-III (including HST).
Including a new version of what seems to have sadly become a laughing stock for some on here (despite running for 25 years), the Brighton-Manchester.
Service pattern:
Hourly IC service from Brighton, calling Gatwick, East Croydon, Clapham, Kensington, Watford, MKC then (alternate hours) Cov/International/New St and (alternate hours) Nuneaton, Crewe, Stockport and Piccadilly (stops with significant interchange potential have been chosen). To answer the usual criticism that there aren't hordes of Brighton residents wanting to go to Manchester, it wouldn't just be about the Brighton market: all sorts of intermediate flows could be catered for with such a service.
Hourly Bournemouth service, diverted after Oxford along EWR to MKC thence northbound up the classic WCML. Services alternating between Manchester and Scotland.
In addition, hourly Southampton-Birmingham to be retained via the classic route, part of a half-hourly Reading-Birmingham with the other 1tph starting back from Paddington. Paddington to Oxford "shorts" to be withdrawn as they would be covered by this service.
Half-hourly "classic Euston-Birmingham" service to be retained.
Something like this would finally give some much needed excitement to the XC network, which has, since Arriva took over, become moribund and unexciting.