According to the live chat I had today on the Eurostar site, they will be doing points maintenance on that day. I wondered why there was NO availability for any train all day, this far out. The rep did say that they may schedule trains for part of the day as that date nears.
Just thought I'd give a heads up for anyone making plans to travel on that date. We looked at alternate modes (plane/ferry/bus), but frankly didn't like any of them. So we'll just change our hotel reservations for a few of our stays, adding an extra day in London so we can leave a day later, and reducing a day in one of our later cities. Arrgghh.