I thought it was 10x26m they were asking for (but I may be wrong here!)
You might be right, but 10x24 is a lot closer to that than 7x26!
Aren't the 807s for indirectly replacing voyagers on services other than North Wales too?
Yes and no. The idea was that reducing the fast Birminghams to 2tph and speeding them up would mean there were enough Pendolinos to work everything other than North Wales - this has near enough already happened, there might be the odd Voyager diagram on a Birmingham but not many. The third service would then be added back as the semifast. If that service isn't added back, they aren't needed. The second Liverpool was entirely separate - as it happens the current one runs in that path and the Pendolino one doesn't run, but that's a bit moot.
I suspect that, if/when avanti get their mess together, demand will increase similar to on LNER, and a second liverpool (and possibly third birmingham) will in fact be justified.
I doubt it. A second Liverpool was always political, it's never really been justified, partly because of Liverpool's very small hinterland, and partly because a fair bit of traffic in that hinterland goes to Wigan NW, Warrington BQ and Chester instead, with capacity at the latter being increased significantly because 10.805 has a LOT more capacity than 10.221, it's something like half as much again, so people will be being priced into going that way.
And the political end could be satisfied by way of the much cheaper LNR service.
So my view remains, these two services will never run, and so the 807s are basically spare, and the cascade I mentioned (807 -> Manchester Airport to Scotland under Avanti, 397 -> LNER) would solve several problems at a very low cost.