So in the summer peaks, 2x5car go to PNZ, simples
Exactly. Or operate one of the seven 9-car trains on those services.
Does anyone really think that there will be spare stock lying around to strengthen "summer peak" services. If a service is diagrammed for a single half length train then I predict that this is exactly what will be provided.
Previous experience of new shorter trains on other routes suggests that these will be procured in just barely sufficient numbers to cope with the AVERAGE passenger flow under ideal conditions.
I recall full length trains on the Waterloo to Exeter line being downgraded to 3 car
DMUs▸ , it was stated that "flexible train length" was a great merit of the shorter trains and that "6 car or even 9 car trains could run at busy times" in fact single unit operation and severe overcrowding was the norm for at least 10 years. Whilst it is true that the 3 car and now some 2 car units do regularly run in multiple this has taken at least 10 years and perhaps 20 years and has barely kept up with passenger growth.
Broadly similar arguments apply to the (then) virgin voyagers, new and very expensive half length DMUs that resulted in overcrowding. These can indeed run in multiple to provide a full length train, but single unit operation is the norm even in the Summer peak, no matter how busy. "not enough spare stock"
"we cant provide extra trains just for a few weekends a year"
"there is plenty of room on some trains"
"we are a victim of our own success, more and more people are choosing our wonderful trains"
"you are recommended to book a seat"
And so on, maybe this lot of new shorter trains will be better, but previous actual experience does not fill me with optimism.