The Kent Route Study has been published
The full study can be read by following this link. https://cdn.networkrail.co.uk/wp-content/uploads/2018/06/South-East-Kent-route-study-interactive-version.pdf .
Towards the end of the study is some very interesting information about possible changes to the MarshLink to enable through running of High Speed services to St Pancras. It seems that a target date of 2024 is feasible but I have not had time to read the Study in detail.