If part of the 222 fleet could transfer to XC that would be a huge step in the right direction for XC... It may be the new franchise that does this though as Arriva don't seem keen on splashing the cash on meeting demand.
Off topic I nkow, but there are a few problems with the 222's going to XC.
Firstly as they stand they can not run with the XC 220's and 221's and although this can be overcome, why would they bother when there are very likely to be up to 20 sets of 221's from ICWC which they can use.
Also, XC would have to wait longer to have the 222's than they would for the sets from ICWC. It could be possible to have the 221's for the Decemeber 2017 timetable change, whilst the 222's are unlikley to be free until at least the December 2019 timetable change. That's 2 years more to wait.
By the December 2019 timetable change it should be possible to run a service, probably Manchester to Southampton (with the Bournemouth leg transfering to the services from Newcastle), with EMU's. In which case the 22x's which currently are used for this service can be used to strengthen other services. Although one service doesn't sound a lot it is likely to need 9 sets, which added to any 221's from the ICWC franchise it could result in a similar number of sets to what would be possible from getting all the 222's (although less coaches). However if the EMU's were run as 7 coach sets they would have a similar level of capacity as 2x4 coach 220's running together, which would more than offset the "loss" of coaches from not getting the 222's.
Depending on what happens with electrification in CP6, XC could be in a possition where they could have a whole load more EMU services. For instance with a little under 120 miles of electrification all the south coast XC services (i.e. Bornemouth to Manchester reinstated fulley and Southampton/Reading to Newcastle) could be run by EMU's. Add in about a further 120 miles (Birmingham to Bristol/Cardiff) and Cardiff/Bristol Temple Meads to Manchester Piccadilly could be run by EMU. With both of those it would also be possibe to run Cardiff Central to Nottingham by EMU as they use lines which would have been wired up by the two lots of about 120 miles. That's then a lot of services which could be run by EMU rather than the current trains.
Yes it is likely that XC will need some form of diesel traction post 2035 as it may not be possible to wire up all their routes by them, but then the 222's would only likely gain about 5 years pver the other 22x's and maybe avaliable again by then anyway.
Also, a small changes to the sets being sent out can lead to some fairly noticable changes in the number of seats. For instance, if you change a 220 for a 221 then that is an increase of seats from 200 to 250 (one extra coach), change a 221 for a pair of 220's and that is an increase in seats from 250 to 400 (three extra coaches) and change a pair of 220's for a pair of 221's and that is an increase in seats from 400 to 500 (two extra coaches). In doing so it is possible for XC to have a noticable increase in the number of seats that they have with very few extra coaches. Therefore, we then need to look at how many extra coaches XC would be getting.
It is likely that (although XC need more coaches) an additional 143 coaches (the 222 fleet) would be a little exsessive and that up to 100 coaches (ICWC's fleet of 221's) would probably provide ample extra capcity, as at about the same time it would also likely be getting some EMU's. As the current XC fleet is made up of 250 coaches. Even just 10 extra 221's (50 coaches) would provide an extra 20% more coaches, whilst 15 extra 221's (75 coaches) would provide an extra 30% more coaches. Whilst if you added all the 222's then that would be an increase of over 55% more coaches.
Which could come along just as there start ot be EMU's coming along to (10 sets of 7 coaches would be an extra 70 coaches or an increase of 28% on the existing fleet and that leaves only one spare and a very tight turn around on the services, so there is likely to be more than 10 sets, also add to this that it might be in XC's intrest to order longer sets than this early on so as to avoid the problems they have at present), this could mean that with the 222's you'd be looking at an increase in the number of coaches of 85% above the existing fleet (or 100% increase if there were 12 sets of 9 coach ordered as the EMU's).
I would suggest that level of increase would be a little over the top and that an increase of about 60% would be a better level (15 sets of the 221's plus the EMU's), although this could be about 70% if there were 12 sets of 9 coach EMU's ordered (again bearing in mind that more EMU's could be ordered soon after to run services over any additional lines which are wired up).
Of course the new XC franchise could just ditch all their 22x's and opt for bi-modal IEP so they have a standard fleet maybe with a mix of 5 and 9 coach sets (say about 60 x 5 coach sets to replace their 220's and 170's with about 25 x 9 coach sets to replace their HST's and 221's), which means that they don't have to keep ordering lots of small orders of EMU's as more of their network becomes electrified and gives them a few spare for running some new/lengthen services.