If the 222s did go to Scotrail, some reconfiguration would be needed. A uniform fleet of 5-car units would seem sensible, formed DMF, MSRMB, 2xMS, DMS - this would require converting intermediate First Class and composite coaches to a Standard seating arrangement, which I'm assuming is possible but don't actually know one way or the other. I can't see that it would be prohibitively difficult, given that First Class to composite has been done, but you never quite know.
The result would be a fleet of 27 trains with 22 First Class and 238 Standard seats, something of a shortfall compared to a 5-car HST though better than a 4-car. The extra unit wouldn't really help - and in fact total fleet seating would still fall short, at 7,008 vice 7,412 - though it would increase redundancy.
With operation at over 100mph off the cards, the capacity of the end vehicles could presumably be increased, though I don't know how much. Really, though, getting up to the capacity of the HST fleet would need an additional vehicle per set to be obtained from somewhere.
It would also continue the tradition of banishing units that Hull Trains don't want any more to Scotland, which is at least mildly entertaining. Buying Voyagers/Meridians in the mid-2000s would have been nice, though I fear an unlikely use of taxpayers' money.
