Think the plans are to run two units together. One for North Wales and the other for Blackpool splitting at Crewe.
Two 7 cars units would be too long for platforms However a 7 and 5 car could just about fit platforms
They won't run 805+807s in service, they're being cleared for rescue purposes though, that would be 312m long, around 48m longer than a 390/1.
For reference, an 805+807 formation would only fit at:
- Euston P1-4 and 15-16
- Rugby P2 and 4
- Nuneaton P2, 4 and 5
- Coventry P1-3
- Birmingham New St P1-4, 6-12
- Crewe P1 (down only), 6 (either direction for the mainline, down only if going towards Manchester) and 12
- Preston P3
- Chester P3
- Holyhead P1
- Runcorn P1
Prior to the pandemic there were a few Blackpool North to London Euston via Trent Valley Pendolino services, I was under the impression that these would be replaced by 807s with the same calling pattern, unless the plan has changed with the WCML recast and the paths for such a service are no longer available.
There's a path leaving Blackpool at 05:35, which already exists, but, from Crewe, this conflicts with the NWC service during later hours. It's entirely possible that what
@92002 suggested could become a reality, however, I don't know if this is actually planned - the Avanti recast presentation has no mention of this happening.