As well as 'the sake of having a new train' I can think of two other reasons for DfT wanting to completely replace them on the ECML:
- Capacity: a 9-car IEP will have more seats (but are they full anyway?)
- Jobs: more do-not-eat-the-soap sticker-application work for the Hitachi plant
Capacity is the only one which is a deal-breaker/maker in my opinion, and even that could perhaps be fixed (2+10 formation anyone?) at the cost of having a pile of redundant DVTs.
You statement doesn't fit the information I have read. See my post above, pendos and IC225 are broadly similar in terms of energy efficientcy. True the pendos regenerate, but I'm 99.99% sure the RSSB study showed the IC225s were in the same ballpark despite not having regen. I therefore suggest that if you remove the section I bolded your post would be correct. I think I read somewhere though that the cost of retro-fitting regen on the 91s was considered not worthwhile.
Well, 90s provide the required performance today don't they? 91s may not be able to keep time due to their higher-top-speed-gearing, but keeping the 90s ought not to be a problem.