Southeastern have published their proposed 2015 timetables. Although these trains now serve Sandwich through to Martin Mill, it is at the disadvantage to Dover.
Currently HS1 trains terminate and commence from Dover Priory, so that you know you will generally arrive at Dover Priory to find the previous service already there.
Next year these trains will commence at St Pancras, travel all the way around North Kent and then to Dover before continuing to St Pancras. This means trains will have more chance of being late.
Also most of the services will take slightly longer, not good when Dover is trying to get the service down to 1 hour.
http://www.southeasternrailway.co.uk/about-us/latest-news/southeastern-publishes-proposed-2015-timetable/
http://www.southeasternrailway.co.uk/your-journey/timetables/januarytimetable/