Bring on 9 car meridians
Totally unsuitable for TPE for so many reasons, too numerous to list them all.
But here's one: Meridians are
125mph trains with a tilt profile (Yes I know they don't tilt), chosen mainly because the Voyager production run was already running, etc...
There are no more Meridians being produced, and it would be totally crazy to build more.
They are totally unsuitable for the TransPennine route, which usually sees trains restricted to
90mph* - and often considerably less than this.
Also, while TPE are often very busy, it is total madness to suggest they should run 9-car sets.
The Desiros (apart from their weight - but that's another story..) are an ideal sort of train for TPE to use, but more services should be 6-car rather than 3-car.... alternatively it may make more sense for there to be a trailer vehicle added to make the trains 4-car (the depot facilities have been designed with this in mind apparently).
I still think that a more sustainable solution would be electric traction - as discussed elsewhere on this forum, but that'll never happen now.
* To those who say the ECML is 125mph north of York - yes this is true,
but they generally use the slow lines to Northallerton (75mph IIRC), and Darlington-Newcastle has some curves that restrict the speed often below 125, and it would be crazy to have 125mph trains that only reach 125mph very briefly. I think it's a bit 'overkill' going for 100mph, to be honest.