I'm reading the WCML requirement to be vague grouping phrase for the CrossCountry fleet, which by Nov 2019 when the franchise renews will be getting on for 20 years old.
We are often blinded by the continued deployment of the HST's, into thinking that 30+ years is normal, but look overseas to Japan in particular and they are quite happy to replace 20 year old trains. Looking back to when the Voyager fleet were introduced, most of us didn't have mobile data, we lugged around huge heavy laptops, talk of having an hours commute was insane in the north and the growth expectations were pretty grim. Fast forward to Nov 2019 and it's clear that a too small fleet of 4/5 carriage trains won't be good enough to carry forwards. Having said that, I'd like to see fleet expansion on CrossCountry well before a post franchise order, which could be 2021 by the time new trains hit routes - another five years of CrossCountry crush loading is a dreadful thought.
I've said this before, I'm expecting to see the 220/221/222 fleets repurposed, either as refurbished 7-10 car fleets or perhaps a bit out the box, re-engineered as 90/100mph capable 156/158 replacements (derated power, seats in the whole of the driving cars, fitted out for regional use) - however this is looking increasing less likely given the new fleet orders and notices buzzing around.