I took some pictures on Friday of the rebuilding work on Waterloo
platforms 20-24, formerly used by Eurostar:

https://www.flickr.com/photos/reclin...57673819851723

You can see how the buffer stops are being moved back 50m, to make
space for a new concourse and gate line (of course, e* trains are much
longer than any trains that will use these shortened platforms in the
future). The ramps at the platform ends are being demolished. The old
Eurostar concourse was at the lower level, which I believe will now be
converted into more retail space.

You can also see how the Eurostar platforms are a couple of metres
higher than the old ones, and I think this will remain the case.
Indeed, they may even be raised a bit more, to British rather than
European platform height, to facilitate step-free boarding. The bridge
over the new retail space, from the old concourse to the new one
(built over the eastern ends of the e* platforms), will therefore
slope up, which you can just about see in NR's artist's impression.

More surprisingly, I saw them laboriously removing and craning out
some of the large glass panes in the canopy. I'm guessing that this is
to get better access to the platforms during the construction work,
unless it's to create a new northern exit. Does anyone know better?

There is a tight deadline for this phase of the work, as platforms
21-24 will need to be used for 23 days in August 2017; they'll then be
closed again, till the project concludes at the end of 2018. Platform
20 will permanently return to use from February 2017, accessed as
before via platform 19.