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HS2 | Euston with only 7 platforms is not fit for the future network, experts say
(www.newcivilengineer.com)
It's not stated explicitly in the article, but my take is that the 7 platform Euston design is basically predicated on the assumption that Old Oak Common will be the "main" London terminus, with only a minority of services extended to Euston.
Which...well, I guess it's not complete insanity, but it is ridiculously short-sited.