Eurostar's new trains mean that from December 2017, they will be providing a twice daily service from London to Amsterdam. The total journey time is expected to be 3 hours 50 minutes (so, say, 4 hours door to door). Trains will have intermediate stops at Brussels, Antwerp, Rotterdam and at Schipol Airport. The return, Amsterdam to London service will not stop at Antwerp.
This service will use the impressive, new e320 trains made by Siemens, which are able to travel over (most) European railway systems.
Journey times from Amsterdam to London are estimated to be a shade over 4 hours which includes a 28 minute stop at Brussels for the purpose of the security checks.
The timetable, at present, indicates a 8.00 am departure and a 5.00-ish pm departure from London, Monday to Friday. Return departures are scheduled to be at 07:48 am and 5.21 pm.
Given that you have to allow an hour to fly to Amsterdam and then, to check in, an hour or so before departure this service could prove very popular especially as the not-quite-so-well served cities of Rotterdam and Antwerp are included. That said, we have no news on fares at this time so viability will mean some pretty clever hard thinking by Eurostar.
Of course, the trains go city center to city center so instead of the lengthy, congested trip to and from Heathrow you alight in the middle of town, rather facing a further journey either along heavily congested roads or on the fantastically expensive Heathrow Express.
The new Siemens trains are compatible with most European rail systems so we can be sure to see many new short haul destinations appearing as capacity permits. Perhaps it is time to consider, rather than a new runway at Heathrow, a new bore on the Channel Tunnel?