Recliner wrote:

I notice that these trains will have "state-of-the-art heating and
air-conditioning systems, look and feel of Tube trains and be
walk-through, without doors between carriages", which sounds just like
the new S Stock trains. Are there any other similarities? I know these
trains are shorter (4 vs 7/8 carriages), but they sound quite similar
in other respects, including where they're being built.

No, there are no similarities between the Underground S stock and the class
378 Electrostars. The 378 is very much a suburban main-line design (the
almost identical class 376 has been operating on SouthEastern suburban
services for the past three years). I'm not sure about the "without doors
between carriages" bit, though, I'm sure that the 376 has doors either side
of the corridor connection. Perhaps it's felt that with such a regular
stopping pattern any draughts from the corridor connection would not be
significant.