It would also have platform issues at places like Reading and Newcastle where XC use 5 car bays. Of course this would also affect the standardised 7 or 8 car units people push in these threads…
Reading has plenty of other platforms, and so isn't an issue, with the current services (5 a day) Newcastle might not be an issue and if we're gong for a new fleet a few extra units would facilitate extending to somewhere with suitable turn back capacity (Middlesbrough being a possible option).
It would be a big deal at Newcastle, at least.
May be, but with a new fleet an extra set or two might allow Newcastle to be served but not the end of line.
My own personal thoughts regarding using Mk3/4 coaches (as well as the stored 221s and even the 180s) is based on the (irritatingly on the nose) assumption that the DafT and XC will not open up the purse strings for new trains. I think XC would benefit from bimodes like the 8xx series.
The thing is the cost may actually be less, especially if your start to include the 6 coaches in store (as that will increase the fleet size by 9.6%).
That's enough that if the following unit costs were used:
Current fleet unit cost of 100 - 31,200
+ 6 stored fleet unit cost of 100 - 34,200
Original 5/9 coach fleet unit cost of +10% giving us 110 - 33,440
Now whilst that means that the lease costs are lower than the +6 stored the total costs might also be cheaper than the current fleet (staff costs, fuel costs, maintenance costs) whilst giving a significant capacity uplift allowing for far more passengers to use the services.
As such, and potentially eveb without banking on future passenger growth or very low passenger growth, it may be cost neutral to get new trains and so it's hardly a case of opening the purse strings to get new trains.
Bottom line, all I'm suggesting is that the powers that be willing to ask for the actual costs so that an informed decision can be made.