Sorry for the further thread drift but to return to Eurostar I think an additional concern is the introduction of the ETIAS visa in late 2023.
EU's Entry & Exit System May Bring Logistical Concerns, Several UK Firms Warn - SchengenVisaInfo.com
The article suggests that accommodating the new machines will lead to space constraints and logistical challenges at ports like Dover and within the confines of St Pancras.
I suspect there is an element of "they would say that wouldn't they" here. Also the article was much earlier in the year so things may have moved on but I have a recollection this was cited as a reason for delaying the reintroduction of Ashford and some of the lower frequency routes.