AFAIK, the 450s mostly run in 8 car formations, so this could be a lengthening of sets to 5 car. There are 127 450s, of which 99 are in the 450/1 original config, so the 100 new vehicles could be to extend all those to 5 car ?
Although since the other 28 are the High Density config logically it would be those services that would go to 10 car ops first ?
Given Southern operate 12 car Electrostars, I assume loadings on SWT are lower such that going upto 10 is sufficient growth ?, or will we see further in future? I guess what I'm getting at is that a bunch of extra 4 car sets would permit easier/more flexible 12 car formations in future rather than starting from a bunch of 5 car sets (and presumably going to 6 car sets).
[In peak max effort this is, I assume smaller off peak]
If the Scotrail 110/125mph EMU goes ahead, which logically would be a "384/5" based on the newer 380, could SWT benefit from some additional AC IC types (once some wiring is up) ? A large order to cover Scotrail, SWT, TPE and perhaps also XC could be a goer?