In an ideal world and planning for future growth so we don’t end up with more ludicrous overcrowding in a few years time, Cross-Country needs a new fleet of 11 car trains - nine standard class and two first.
The thing is, XC could build up to that fairly easily without having to scrap all the 22x's early and without the cost of running 11 coach trains on services which only have about (say) 7 coaches worth of passengers now (4 coach full and standing is probably about 7 coaches in a bit of comfort).
Get their fleet to be made of:
12*9 coach 80x (or similar)
43*6 coach 220/221's
The latter works if you scrap some end coaches (which are generally only about 1/2 the capacity of a middle coach) and reform with a half decent number of seats.
You could do that by placing an order to lengthen the GWR 802's to 9 coaches, GWR retain the ability to run 12 full length services (22*5 coaches is the equivalent to 11 full length services) with 10 transfering to XC as well as 2 new 9 coach sets (106 coaches in the order). You then have an option so you could order more units for XC so if there's growth (spoiler there's likely to be) you could then have more 9 coach units ordered (either for GWR and/or XC and/or TPE).
That'll give you about 10 years before a decision is needed on if you need a full 11 coach fleet for XC, but would give you the ability to order more units to be delivered for up to about 6 years.
If it could be properly managed XC has colossal potential to build both standard and first class business. However, this will never be realised while the organisation remains shackled to the DfT and state ownership.
The above option wouldn't significantly increase the number of coaches (GWR -2 coaches, XC +44, giving a net increase of 42 coaches - when the current number is coaches at XC and in the GWR fleet is 432, so about +10%, XC going to a full 11 coaches fleet would be at least +50%) on lease, but does increase the number of seats by a noticeable amount.
However, without access to the GWR fleet (which is likely only the state could do, or at least require two companies to allow) it would require GWR to keep paying for extra coaches (22*5= 110 vs 12*9=108, even though GWR would have more seats from the.
Cross Country should be a fully privatised open access operator, free to build a successful business to meet the demands of the market and drive growth, as indeed should all long-distance Inter-City operations be ideally.
Hopefully a change of government eventually will totally free up the long-distance passenger business, leaving just a few commuter/urban/metropolitan services under the control of local transit authorities.
The thing is, there'll still be national government involvement - even if that's to determine who gets to use what paths.
Also, where does GWR sit, it's certainly for long distance passengers but then through Devon and Cornwall many of those provide the local transport? However it also provides a lot of commuter/urban services (to answer would probably mean a new thread).
Sadly for now, we are regressing back to allowing the ‘we know best’ nanny state to play with the train set. Investment will dwindle to just a trickle, when the government has health, education and defence to support first.
So, do I think GBR can bring Cross-Country back to INTERCITY standard. Not a chance, cross country services will wither away, just as the did under the previous misguided period of nationalisation presided over by British Rail.
However, there is a path (as suggested above) where even with government investment dwindling there could be a way to increase capacity without significant extra costs. Maybe not as much capacity as some might like, but then it's unlikely that a private company would increase the fleet size by +50% without some assurances that they'll see a return on that investment.
Just because XC saw 15% growth in passenger numbers last year and 18% the year before as well as it only needing about 8% growth before carrying more passengers than pre COVID isn't enough.
Especially given the opening of HS2 may alter demand (Reading to Birmingham, let alone further is likely to be slightly faster via HS2 and more frequent at 3tph vs 2tph), which is a risk factor for a private business which is likely to limit their desire to invest in trains with a 35+ lifespan when in 12 years time things could be quite different.
Conversely, by part using the GWR fleet and reforming the 22x's that would allow government to place a like for like order in (say) 2035 (so broadly as HS2 opens) to replace the 22x fleet, but with options to lengthen depending on how HS2 impacts XC.